vol. 6 1911/12

BAND VI HEFT 1 u. 2 OKTOBER 1911

ZEITSCHRIFT

FÜR

INDUKTIVE ABSTAMMUNGS- VERERBUNGSLEHRE

HERAUSGEGEBEN VON

. CORRENS (münster), V. HAECKER (uatte), G. STEINMANN (sonn), R. v. WETTSTEIN wien)

REDIGIERT VON

E. BAUR certin)

o

BERLIN

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1911

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NOV 29 1911

The Mendelian Inheritance of Certain Chemical Characters in Maize’).

By Raymond Pearl and James M. Bartlett.

Introduction.

In the work which has thus far been done along Mendelian lines in the study of inheritance the characters dealt with have been, in the main, either purely structural, or else somatic colors and color patterns. Beyond all structural and color characters there is, a further, more or less well defined, set of attributes of organisms, the inheritance of which has not been subjected to experimental analysis so far as we are aware. These may be called the invisible chemical characters. In all agricultural work these characters are of great importance. Thus to mention but a few examples; the value of sugar beets is directly determined by their sugar content; maize is of value for feeding purposes in direct proportion to its nitrogen content, etc. It is, of course, a well known fact that different strains and different individuals within the strain, in all our agricultural plants, vary in their chemical composition. On the basis of this variation a great deal of work has been done in improving various plants by selective breeding in respect to one or another of their invisible chemical characteristics. One needs to mention here by way of illustration only such conspicuous examples as the breeding of beets for increased sugar content, and the work at the Illinois Station (1)?) in changing the protein and oil content of maize by selection. It may fairly be

1) Papers from the Biological Laboratory of the Maine Experiment Station, Orono, Maine, U.S. A. No. 26. The investigations on which this paper is based were carried out in the biological and chemical departments of the Station working jointly. The division of labor was as follows: The work of obtaining the material and the preparation of the paper were done in the Department of Biology; the chemical analyses were made in the Department of Chemistry.

2) Numbers in brackets throughout the text refer to items in the literature list at the end of the paper.

Induktive Abstammungs- und Vererbungslehre. VI, I

2 Pearl and Bartlett.

said that in such cases as these is to be found what is apparently the best existing evidence that the continued selection of minute fluctuating variations has a cumulative effect. It is, therefore, of the greatest importance to subject this evidence to the most careful scrutiny, and to make a thorough experimental analysis of the method of inheritance of these invisible chemical characters.

It is the purpose of the present paper to give the results of a study of the inheritance of certain invisible chemical characters in maize. The problem dealt with is this: Do such characters as the nitrogen content, sugar content, starch content, ash content, etc., of maize behave as unit characters, showing the Mendelian phenomena of dominance, recessiveness and segregation? If they do so behave another category of attributes of living things will have been shown to conform to Mendel’s fundamental generalizations. Correns (13) in his classical memoir on maize hybridization and other workers have dealt with starchy and sugary endosperm, but not with the segregation of other chemical characters.

Material and Methods.

Since 1907 the Department of Biology of this Station has been engaged in the experimental breeding of several strains of maize. Two of these furnished the material for the present investigation. One of these was a fine grained, white, sweet (or “sugar”), maize (Zea mays saccharata). The other was a yellow “dent” variety. Both were unnamed varieties. In the work of the Station they have been given respectively the names of their original growers from whom the foun- dation stock for the breeding experiments was obtained. The sweet corn!) used in these crossing experiments has been thus designated as “Dennett”, and the dent corn as “Cornforth”. These names have no significance except that of convenience in reference.

A detailed account of the history and characteristics of sweet corn of the Dennett strain has recently been published (2) and need not be repeated here. It may merely be said that the corn is a fine- grained, early maturing, white sweet corn, bearing ears of fine quali- ty2). It has been rather closely inbred for a long time (15 to 25 years)

1) The word “corn” is used in this paper in the American sense, meaning “maize”, and not in the EnglishTsense, meaning “grain’’.

2) Corn of this strain and from seed bred in the Experiment Station plots took first and second prize in the world class for sweet corn at the National Corn Exposition in IgII.

Ww

The Mendelian Inheritance of Certain Chemical Characters in Maize.

and breeds remarkably true to type. The appearance of a typical ear of the sweet maize used in the crossing experiments is shown in die TA,

The dent corn used in these experiments was an unnamed strain which has been grown for a long period of years (at least 15) by Mr. Hiram Cornforth of Waterville, Maine. It is an early maturing yellow dent, producing ears of fair size, but not very uniform quality.

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Fig. 1. Photographs of the maize discussed in the text. A Pure sweet parent race. B Pure dent parent race. C Ear bearing F, progeny kernels from the cross of A with B. The ears bearing F, progeny kernels are indistinguishable in appearance from the pure dent parent ears (B).

It has been inbred for a long period, all of the corn forming this strain being descended from a very few original ears. Is has never been specially selected for uniformity with respect to shape of ear, size and shape of kernel, etc., and on this account varies to some extent with reference to these characters. The appearance of a typical ear of this yellow, dent maize is shown in fig. 12.

Both the dent and the sweet corn used in these experiments are

known from direct experimentation and observation on the part of 1*

4 Pearl and Bartlett.

the writer to breed true to their respective types. That is, the sweet corn used never throws starchy kernels, nor does the dent ever throw sweet kernels.

In the summer of 1908 some of this dent corn was planted on the sweet corn breeding plots of the Station at Farmington, Maine. This planting was done in such a way that a sweet corn plot, approximately an acre in extent, was bounded on two parallel sides by this dent corn, there being two rows of the latter on each side of the field. As fast as tassels appeared on this dent corn they were removed!), before the staminate flowers had opened and shed any pollen. The detasseling was done with the greatest care, not merely because of the safeguarding of the crossing experiments, but also in order that none of the sweet corn, which was being pure bred for another and different purpose, should be fertilized with pollen from the yellow dent. As a matter of fact, only the very smallest amount of pollen escaped from the yellow dent corn. From the whole acre of sweet corn there were obtained only a very small number of kernels (less than 25) which had been fertilized by yellow dent pollen. The total number of sweet kernels produced was somewhere in the millions. The amount of such pollen loose in the field was negligable for present purposes.

The ears borne on the yellow dent stalks were fertilized by pollen from the sweet corn, and in consequence the kernels of these ears represented the F, seed of a cross in which the sweet corn was the d, and the dent corn the 9 parent. All of these kernels were like each other and like the yellow dent parent in appearance. This is in accord with the well known results of Correns, Lock, East and others demon- strating that in maize yellowness and “starchiness” of endosperm are dominant over whiteness and “‘sweetness” (3). The appearance of ears bearing these F, seeds was exactly like fig. 13. Several bushels of such ears were grown in 1900.

In 1909 Dr. Owen Smith?) of Portland very kindly offered to plant a large plot of this F, cross-bred maize at his farm on the shore of Sebago Lake. Two acres were accordingly planted with F, seed, producing F, plants, which in turn bore F, kernels. This

1) By Dr. Frank M. Surface, who carried out the main part of the field work in corn breeding in 1908.

2) It gives me great pleasure to express both the indebtedness and thanks of the Experiment Station to Dr. Smith for his aid in this and other plant breeding work carried on during the last four years. R. P.

The Mendelian Inheritance of Certain Chemical Characters in Maize. 5

plot was in an isolated locality far removed from other corn, and in a situation such that in addition to distance natural barriers acted to prevent the entrance of foreign pollen. No attempt was made to control pollination within the plot, so that what happened was a free and general crossing of the F, plants inter se. Since the original parents were a white sweet and a yellow starchy corn the Mendelian expectation here is that the F, kernels resulting from the free and random intercrossing of F, gametes will be of four different kinds (viz. yellow starchy, white starchy, yellow sweet and white sweet) in the ratio of 9:3:3:1. This is apparent if the gametic formulae be worked out. Let Y yellow endosperm y absence of yellow white endosperm S starchy endosperm s sugary endosperm!). Then in the P generation we have YS- YS yellow dent (starchy) parent ys-ys = white sweet parent. When crossed these give in F, YS-ys yellow starchy F, kernels, there being domi- nance of the characters. These F, kernels produce plants which make gametes of the following kinds: YS, Ys, yS, ys. These mated at random give F, kernels of the following sorts:

2 YS.Ys ı yS-yS ! 3 white starchy 2 YS-yS 2 yS-ys

2 YS-ys } = 9 yellow starchy ıys-ys = I white sweet 2 Ys-yS ı ¥s- Ys 3 yellow sweet. ı YS- YS 2 Ys-ys

As a matter of fact extensive counts gave a reasonable approxi- mation to the expected 9:3:3:1 ratio. Fig. ıC shows an ear bear ing F, kernels. The corn on Dr. Smith’s farm made a good growth but owing to seasonal and cultural conditions matured rather une- venly. After it was harvested a sample of about two bushel of ears was sent to the Station. This was a random sample of the crop. Over 50 of these ears (taken at random) were shelled and the kernels

1) We will not stay here to consider what it is that s denotes the absence of.

Let us for the moment regard the notation as merely a symbolic expression of the observed fact, without ulterior implications.

6 Pearl and Bartlett.

sorted into the four different kinds found on each ear. From each of the four lots so obtained random samples of about a pint of kernels each were withdrawn to furnish the material for the chemical analyses of the F, generation. Samples of the P and F, generations were drawn at random from large supplies of thoroughly mixed seed of these generations which were on hand for other purposes. All of the corm used in the chemical work was entirely mature and thoroughly air dried.

It remains now to speak of the chemical methods used in this study. The following determinations were made, in duplicate, for each sample after it had been finely ground: 1. moisture, 2. nitrogen, 3. protein (= N x 6,25), 4. crude fat (ether extract), 5. ash, g. crude fiber, 7. pentosans, 8. sucrose, g. dextrose, Io. total sugars, II. starch. The methods of analysis used were those of the Association of Official Agricultural Chemists (4), except that for the determination of sugars the methods employed by Straughn and Church (5, p. 14) in their study of the effect of environment on the composition of sweet corn were used. These latter methods had previously been worked out by Straughn (6) and published in an earlier paper. The actual work of analysis was carried out by Mr. A. G. Durgin, Assistant Chemist.

Data.

The results of the analyses of the parent races and the F, and F, cross-bred progeny are given in Tables I und II. Table I gives the percentage of the different constituents actually found, and Table II gives the percentage which each constituent is of the total dry matter. In Table I the figures for each of the duplicate analyses and the arithmetical average of the two are given. In Table II only the averages appear.

Before entering upon any discussion of the inheritance of these chemical characters it is necessary to compare the analyses of the parent strains used with other published analyses of dent and sweet maize. Two points need specially to be considered here. In the first place, since the whole of the discussion which follows assumes the substantial accuracy of the chemical analyses made, it is desirable to see whether our results agree with those of other workers, on similar material. In the second place it is important to know how far the dent and sweet varieties used in this study as original parent forms, are typical in respect to chemical composition when compared with dent and sweet corn in general. In other words, do the obvious

Table I.

Showing the Percentage Compositition of Yellow Dent and White Sweet Strains of Maize, and of their Cross-bred

Progeny. Z Parents Br F, Progeny F, Progeny BE 5 a Yellow White Yellow White | Yellow White Character 5 Yellow Ee zs 3 Dent Sweet = h Starchy | Starchy Sweet Sweet | Star 3 Ohi 6 paced (9) (3) (3) (1) Moisture 8.56 7-53 9.70 10.71 10.38 | 7.87 8.48 8.54 7-47 9.67 10.58 10.18 RT 8.31 Av. 8.55 7.50 9.685 10.645 10.28 7.795 | 8.395 Nitrogen TR i S778 1.51 Tio2 ri; 1.80 1.79 1.52 1.77 ART 7.64 07159 E80 1.78 Av. 82 1.775 1.51 1.63 1.585 1.80 1.785 Protein 9.71 11.36 9.65 10.35 10.10 | 11.50 11.44 9.71 fe cae ire 9.65 10.48 10.16 11.50 11.37 Av. 9.71 | 11.335 9.65 10.415 10.13 II.5O | 11,405 BER = se ae a he 2 ee 1 Crude Fat 3-91 8.32 4.20 4.52 | 5.01 7:85 8.33 3.91 8.36 4.37 4-47 5.05 7.35 8.33 Av. 3.91 8.34 4.285 4.495 5.03 7.85 8.33 Ash 1.45 1.93 1.32 1.33 1.35 1.80 1.79 1.45 1.94 1.28 1733 1.34 1.82 2.77, Av 1.45 1.935 1.30 1.33 1.345 1.81 1.78 Crude Fiber 1.96 2.21 1.81 TOGO RT, 2.35 2.22 2.04 ° 2.32 1.75 1.64 | 1.65 2.48 2.28 Av. 2.00 | 2.265 1.78 1.665 1.695 2.415 2.25 Pentosans 6.35 | 6.64 5.39 5-33 5.39 7.52 | 7.34 6.26 6.64 5.27 5.29 5-30: | 7255) 1 ,,7:34 Av. 6.30 | 6.64 5-33 5.32 5.345 7-535 7.34 Sucrose 1.41 | 3.04 1.67 2.07 1.73 4-95 4.40 144 2.89 1.68 2.10 | 1.66 4.99 4.40 Av. 1.425 2.97 1.625 2.085 | 1.695 4.97 4.40 Dextrose [e) 1.63 0.08 [e) [e) 3.12 3.12 fo) 1.57 0.16 o fe) 3.16 3,32 Av. fo} 1.60 0.12 [6) fo) 3.14 3.22 TotalSugars 1.41 | 4.64 1.69 2.07 2:73 8.09 7.62 1.44 4.49 1.80 2.10 | 1.66 8.13 7.62 | Av. 1.425 4.565 1.745 2.085 1.695 8.11 | 7.62 Starch 60.80 53.82 60.05 58.63 58.63 50.44 49.77 60.80 54-31 59.60 59.13 58.86 50.44 49.77 Av. 60.80 54.065 59.825 58.88 58.795 50.44 49.77

8 Pearl and Bartlett

Table II.

Showing the Analysis, Calculated as Percentage of Total Dry Matter, of the Samples of Maize Given in Table It).

Parents F,-Progeny F,-Progeny Yellow | White Yellow, White | Yellow White Character Dent Sweet ul Starchy Starchy Sweet | Sweet ei oe ©) |G) | Gale Nitrogen. acme iiscine | 1.66 | 1.92 1.67 1282010 2.77, 1.95 1.95 Protesuer E22 Db 6 10:62 | 12.25 10.68 11.66 11.29 12.47 | 12.45 CruderBatser arenes 4.28 | 9.02 4.74 5.03 5.61 | 8.51 9.09 EL Seda 0702000.0.0.0 1.59 2.09 1.44 1.49 1.50 | 1.96 1.84 Crude Fiber 2.19 | 2.45 1.97 1.86 1.89 | 2.62 | 2.46 Bentosansse EA 6.89 | 7.18 5.90 5.95 | 5.96 | 8.17 | 8.01 Sucrose ee 1.56 | 3.21 1.80 2.33 | 1.89 | 5.39 4.81 Dextrose SER Weikelhe le [6) | 08775} 0.13 fe) | fe) 3.41 3.52 Total Sugars. ..... 1.56 | 4.94 1.93 2.38 1.89 | 8.80 | 8.32 Seid 6 6 665 RE Gans | Gag 66.24 65.89 | 65.53 | 54.70 | 54.33

and striking chemical differences between the two parent forms shown in Tables I and II represent real and typical varietal differences, or are they merely the insignificant and inconstant vagaries of seasonal conditions, random sampling, chemical analysis, etc.? To the agri- cultural chemist, familiar with material of this class, this question will doubtless seem foolish. The biologist will want evidence, however, since the phenomena with which he is immediately familiar furnishes him no basis on which to form a judgment as to whether, for example, a difference 0.2 or 0.3 percent in nitrogen content is significant or not.

Table III gives comparative data from which conclusions on these points may be drawn. These data are taken from various compilations which have been published.

From this table we note at once the following points:

I. The parent strains of yellow dent and white sweet maize used in these crossing experiments agree in their chemical compositions with average analyses of large numbers of samples of dent and sweet varieties. This agreement is as close as could reasonably be expected, when such facts as environmental influences, random sampling, etc., are taken into consideration.

2. It is evident that the differences in chemical composition between dent and sweet varieties shown in our parent strains are typical of these varieties in general, and are not of a fortuitous

1) Only the averages are computed.

The Mendelian Inheritance of Certain Chemical Characters in Maize. 9

Table III. Comparative Analyses of Dent and Sweet Maize, r Dent Maize Sweet Maize 78 3 | [Parent yellow | | Parent white

dent strain sweet strain

lat) | IIa?) | IIL)

Constituent It) | II?) Heal in | aan present work | present work

Molsturer «5. + + „| 10.56 | 10.14 | 8.55 8.82 | 8.70} 9.45 | 7.50 Braten ce ee. «1 10:25) 0:36:} 9.71 1.62 | 11.43 | 11.41 | 11.335 Mende Pat... css 5.02 4.96 3.91 8.13] 7.79 | 7.76 8.34 Ash s Ao 8 1.53 | 1.47 1.45 292.1 Tor 1.77. 1.935 Srude Fiber ... . 2427, 22m 2.00 2.79 2.86 | 2.22 2.265 Benfosans . a... = |= | | 7.01} 6.64 SNGEOSG%) 6 a 5 6 «3 4) oo u | 2.94 2.97 INEXTEOSE) 5 = oes oo _ _ = || = 112 1.60 otaleSupars) a. _ | 4.04 4.505 SIEAUGO ells kanal |) || = |) = 56.25 54.065 Total carbohydrates | |

other than crude |. | | |

EIDeEZ cl. 2221 70:40)) (68:65 68.525 66.72 | 62.76| 67.30 65.27

character, nor due to errors of analysis. Summarized these differences are as follows: air-dry sweet corn in general carries less moisture than dent corn, sweet corn in general has a higher percentage of protein, fat, ash and fiber than does dent corn in general. On the other hand dent corn in general has a higher content of starch and other carbo- hydrates with the exception of fiber and the sugars than does sweet.

We may now consider the results regarding the inheritance of chemical characters in maize which appear to flow from the data set forth in Tables I and II.

F, Generation.

In general it may be said that the F, kernels resemble most closely the dent parent in their chemical characters. In other words

1) Analysis I represents the average of all analyses of dent varieties of maize by Jenkins and Winton (7) p. 95. Analysis Ia represents the average of all analyses of sweet varieties compiled by the same authors (p. 99).

*) Analysis II and Ila are taken from Wiley (8) who gives them on the authority of König. II represents the analysis of 149 samples of dent maize and Ila the analysis of 27 samples of ‘sugar corn’.

3) Analysis III gives the mean result from 41 samples of sweet corn tabled by Straughn (6). The means in Table III are our own calculations from Straughn’s figures, since that author gives average figures on a water free basis only.

Io Pearl and Bartlett.

there is a definite tendency towards the complete dominance of the chemical conditions found in the dent parent over those found in the sweet parent. This dominance is by no means perfect in all characters, however. In particular the F, kernels are plainly intermediate between the two parents in respect to sugar content, both of reducing and cane sugars. In respect to ash, crude fiber, and pentosans the Fy kernels run distinctly below either parent. In general it appears that with respect to these chemical characters of maize, as in so many other cases, the F, heterozygotes are distinguishable from the parent bearing the dominant character. The F, kernels in these experiments are not to be told by visual examination from the pure dent parent, yet a chemical analysis shows that they really are different, lying close to this parent, it is true, but still in a definite degree inter- mediate in character between the two parents.

This result in F, is of interest in connection with the statement made by Webber (12) to the effect that (loc. cit. p. 32): “In the writer’s experiments, however, particularly in the case of dent races with starchy endosperm crossed with sugary races with sugary endo- sperm, there has been no indication of a modification of the chemical constitution.” Careful examination of Webber’s paper fails to discover that this statement was based on any exact analytical data. Rather it was apparently based simply on the external appearance of the grains, which is, as has been said, like that of the pure dent parent when the sweet corn is the G parent. The present results show clearly enough that the F, (heterozygote) endosperm is distinctly different in chemical composition from either of the pure parent forms, containing, for example, more than a fifth more sugar than the pure dent parent.

We may turn next to the

F, Generation.

At the outstart attention should once more be directed to the fact that all of the kernels whose analysis is headed “F, Progeny” in Tables I and II came from the same ears. That is to say the yellow starchy kernels, the white starchy kernels, the yellow sweet kernels and the white sweet kernels in the F, generation all grew upon the same plants and upon the same ears. Therefore, the environmental conditions under which they obtained their development were as nearly identical as it is possible to get. Such differences between these kernels as appear in the analyses cannot be accounted

The Mendelian Inheritance of Certain Chemical Characters in Maize. II

for by environmental differences or by differences in the handling or treatment of the seed, but must be due entirely to inheritance. That is to say, the chemical differences observed and recorded in these four columns of the tables mentioned are determined by differences in gametic constitution.

Turning to the results in the F, generation, we may say that in general there is very plainly a segregation in the Mendelian sense in respect to all the chemical characters under con- sideration. In a general way it is evident that this segregation of invisible chemical characters appears to follow or be associated with the segregation of the group of characters which together determine the class of the grain. That is to say, the yellow and white starchy kernels in F, are on the whole alike in respect to chemical composition and different from the yellow and white sweet F, kernels. When a detailed examination is made, however, it is apparent that this simi- larity in chemical composition of starchy (or sweet) kernels among themselves is not complete. In other words, the tables suggest that the invisible chemical characters are inherited in certain cases at least, as definite unit characters not dependent either on other invisible characters or on the visible characters which determine the place of the grains in the general categories which head the table. This matter will be considered in detail in a later section. Each chemical character taken account of in the analysis may now be discussed separately.

Moisture. The tables show that the F, kernels of all classes had a higher moisture content than the corresponding parent or F, classes. This difference is more marked in the case of the starchy than in the case of fhe sweet kernels. Thus, the yellow and white starchy grains in F, are roughly 2 percent higher in moisture content than the original yellow dent parent. The difference between the yellow and white sweet F, kernels and the original sweet parent is distinctly less marked, both absolutely and relatively. The F, yellow and white starchy kernels are roughly about one percent higher in moisture content than the F, grains.

The differences between the different classes of F, progeny kernels in respect to moisture content are noteworthy, when one remembers that all of these kernels were borne upon the same ear and subjected to exactly the same conditions of maturity and drying. The starchy kernels are roughly 2 percent higher in water content than the sweet kernels borne upon the same ears. This means that with an equal

12 Pearl and Bartlett.

degree of maturity and equal period and condition of drying there is a marked difference between the sweet and starchy kernels in respect to retained moisture. Thus, in F, we see clear evidence of segregation in respect to this character, the differences between the F, kernels being exactly those which we have seen to be typical when pure starchy and pure sweet varieties of maize are compared. These diffe- rences in retained moisture after equal extent of drying undoubtedly depend upon physical or structural differences in the kernel, and probably primarily on starch content.

Nitrogen and Protein. Since the figures tabled as protein are, in

accord with the usual custom, derived from the nitrogen determinations simply by multiplying by the factor 6.25 we may consider these together. It is quite apparent that in F, there is a segregation with respect to protein content of the kernels. Averaging in F, both starchy classes together and both sweet classes together we find that the latter run approximately one percent higher in protein content than the former. Actually in the case of the direct determinations (Table I), the sweet kernels are 1.18 percent higher in protein content than the starchy, while the figures in Table II on a water free basis show an excess of 0.99 percent of the sweet over the starchy in respect to protein content. While there can thus be no doubt as to the reality of the segre- gation in F, in respect to this character it is of interest to note that there is an increase in the protein content of the F, starchy kernels of both yellow and white classes as compared with the original dent parent or with the F, kernels. That is, the “low protein’ segregate has a higher protein content than the pure “low protein’, parent or the F, kernels in which “low protein” is the dominant condition. In the case of the sweet kernels (either yellow or white) in F, there is only a very slight and probably quite insignificant increase of protein content as compared with the original white sweet parent. The meaning of these facts will appear in a later section.

A matter of much interest in connection with the matters here under discussion (nitrogen and protein content) lies in the fact this character is in no way directly related to the group of physical and chemical attributes which give starchy and sweet kernels their distinctive characters as such. It is obvious that certain chemical characters must segregate as a part of the complex which gives rise to the external, physical appearance of the kernels. The most obvious

The Mendelian Inheritance of Certain Chemical Characters in Maize. 13

of these characters, of course, is the starch content. The external physical qualities by which one can tell at once whether a grain belongs in the starchy (dent) class or, on the other hand, in the sweet class are in no way directly related to the protein or nitrogen content of the kernels. We may have perfectly characteristic sweet kernels of either high or low nitrogen content and, on the other hand, we may have perfectly good starchy kernels (dent or flint) with either high or low nitrogen content. The analyses given in the present paper, from the nature of the case, do not show this fact, but a study of chemical analyses of maize in general makes it perfectly clear. Thus for example, Straughn (6) in his table III (loc. cit. pp. 48 and 49) gives analyses of different samples of Stowell’s Ever- green sweet corn ranging all the way in protein content from as low as 5.35 per cent through a continous series showing such grades as 6.32, 7.46, 8.07, 8.34, etc. on up to as high percentages as 11.58, 11.41 and the like. On the other hand, extensive analyses of starchy varieties of corn such as those given by Hopkins (9) for dent maize show variations in protein content all the way from about 8 per cent up to as high as 14.92 per cent. Dent corns of higher content than this last figure have been analyzed.

We have in the present results, then, clear evidence of the Mendelian segregation of an entirely invisible chemical character not directly connected in any way with the general complex of chemical and physical characters which give the kernel its characteristic external appearance.

Crude Fat. The facts here are essentially similar to those already brought out for nitrogen and protein content, with some minor diffe- rences. The evidence for the segregation of this character in F, is perfectly clear. The two starchy classes of F, kernels have a crude fat content only a little more than half as great as that of the two sweet classes of kernels in the same generation. We note here again that the crude fat content of the starchy kernels in F, is considerably higher than the crude fat content of the original yellow dent parent. The significance of this fact will appear later.

It is of some interest to note that there is a difference in fat content between the yellow and white classes of both sweet and starchy corn in F,. The white classes (whether sweet or starchy) run a little higher in crude fat content than do the yellow classes. This might be expected as a probable result if, as actually appears

I4 Pearl and Bartlett.

to be the case, there is no close relation between the crude fat content and the general complex of the physical and chemical characters which give the kernels their characteristic external appearance as either starchy or sweet or yellow or white. The same sort of relationship is to be observed in the protein content, although there the differences are not so marked as in the case of the fat content.

Ash. The evidence that there is a segregation in F, in respect to ash content is quite as clear as with reference to any of the other characters, though again ash content is not in any way closely or directly related to the complex of physical and chemical characters which together give a kernel of maize the external attributes of “‘sweetness’” or “starchiness”. An interesting and noteworthy fact in connection with the ash content is that all of the cross-bred samples, whether in F, or in F,, run lower in ash content than the correspon- ding one of the parent forms. The explanation of this general diminution in ash content will appear as we proceed.

Crude Fiber. Here the evidence of segregation in F, is again quite clear. “High fiber” is the recessive character and it is remarkable how closely the “high fiber” segregates in F, agree with the original “high fiber” parent. In the classes showing the dominant (low fiber content) character in F, it is to be noted that there has been a con- siderable reduction in fiber content below that of the original “low fiber” parent. We seem to have here something like the “intensi- fication”? of the character through segregation, which will be discussed more particularly in connection with sugar content. The chief diffe- rence is that here it is the dominant character which appears to be “intensified”? whereas in the case of sugar it is the recessive character.

Pentosans. Here the evidence of segregation is unmistakable, and is made more evident through an apparent “intensification” of both the dominant and the recessive characters. That is to say, the ‘low pentosan” classes in F, have a lower content in this class of carbo- hydrates than the original “low’’ parent and at the same time the “high pentosan”’ classes have a higher content than the original “high” parent. It is further to be noted that the dominants in F, agree very precisely with the F, kernels in respect to pentosan content.

Sugars. The facts with reference to sugar content of the Fy, kernels are of especial interest because these are the characters which

The Mendelian Inheritance of Certain Chemical Characters in Maize. 15

most markedly differentiate the two parent races crossed. That the sugar content (including both sucrose and dextrose) segregates in F, in a Mendelian fashion is evident. This is particularly striking in the case of dextrose. The dominance in respect to this character is not perfect in F,;. Measureable amounts of dextrose are found in the F, kernels, although these are typical dent (starchy) kernels in appearance. In F,, however, there is no measureable amount of dextrose in the starchy kernels.

The most striking result in F, with reference to the sugars is the intensification of the recessive character (high sugar content). The total sugar content of the F, sweet kernels is nearly as great as that of the original parent sweet maize, which is itself well above the average of sweet corns in respect to sugar content. This increase in sugar in the F, sweet segregates appears in both sucrose and dextrose but is relatively greater in the latter. The relatively great amount by which the sugar content is increased in these F, segregates is indicated by the fact that Straughn (loc. cit. Table V, p. 44) in an analysis of 62 separate samples of Stowell’s Evergreen corn with an average total sugar content in the dried seed of 4.04 per cent, finds only 5.44 per cent as the maximum total sugar content in the 62 samples. Our F, segregates average 7.865 per cent (8.56 per cent water free) total sugars in the completely matured and dried seed. It is evident that an extraordinary increase in the total sugar content has been associated here with the processes of gametic mixture and subsequent segregation.

The explanation of this intensification of characters accompanying segregation is not clear. The present case is by no means an isolated one, however. Attention has recently been called (I0) to a similar phenomenon in the segregation of the barred color pattern and comb types in fowls. A more perfect or “intensified’’ condition of the characters appears in the F, segregates than existed in the parent forms. Results of this kind may be due to purely gametic causes (germ variation, gametic “purification” in gametogenesis following a wide cross etc.) or to purely ontogenetic causes (for example more perfect activation of determiners following crossing), or to a com- bination of these causes. The observational basis respecting the phenomenon is as yet much too slender to permit the rearing of any speculative superstructure upon it. It may further be said that we are quite possibly dealing here with an extreme aspect of a pheno- menon which has long been held by practical agriculturists to occur:

16 Pearl and Bartlett.

viz., an improvement or benefit following the introduction of “new blood” into a strain which had “run out”. May it not be that when, as is the case in ordinary “pure breeding” of animals and plants the allelomorphs segregated in gametogenesis are not widely different from one another, there is a gradually declining degree of precision in the segregation? And further may not this precision be regained and the allelomorphic character determiners be separated in a degree of purity not known in their “pure-bred” history, in a gametogenesis involving widely differing characters? All this is, of course, mere speculation. One hopes, however, that it may serve to direct attention to the importance of careful and detailed comparison between F, and sub- sequent segregates and original parent forms, in order that more data may be obtained in regard to this phenomenon of “‘intensification” of allemorphic characters during segregation.

Starch. The starch content shows the same evidence of segre- gation in F, as do the other characters. The two starchy classes in F, agree very closely with each other in respect to this character, as do also the sweet classes between themselves. It is to be noted that both starchy and sweet kernels in F, are below the corresponding pure parents in respect to starch content. This is presumably associated with the fact already brought out that the F, kernels are higher in sugar content than the pure parents. Sugar and starch content are opposed characters in maize.

Do the Invisible Chemical Characters Segregate Indepen- dently as Separate Units?

In what has preceded, only the evidence of a general segregation of chemical characters has been presented. We have now to consider the more difficult and more important problem of whether each one of these is a definite unit character segregating independently of the others. Or do these characters form a general complex which as a whole segregates together? Obviously this is a matter of first rate importance, but it is one which cannot be solved by direct methods. Some consideration will make the reason for this clear. Since there is no distinct and definite relation between the external appearance of a kernel and its chemical composition (except in respect to starch and sugar content) the only basis on which kernels can be sampled for analysis in F, is that of external appearance, which we have used. We can take a random sample of yellow starchy, or of yellow sweet,

The Mendelian Inheritance of Certain Chemical Characters in Maize. 17

or of white starchy, or white sweet. But if nitrogen content, for example, is a single, definite unit character which segregates without regard to starchiness, sweetness, yellowness or whiteness, we should expect that in each of the four F, random samples, taken on the only possible basis (that of external appearance) there would be some kernels with high nitrogen content, and some with low. The numbers of these two kinds of kernels in a random sample would be expected to be in the normal Mendelian ratio. This, then is our problem, to determine whether each of our four F, random samples is made up of kernels bearing dominant and recessive conditions of invisible chemical characters in regular Mendelian proportions.

A strong suggestion that something like this is the fact arises from