36 DIMORPHIC LEAVES IN EELATION TO HEREDITY. 



example, the purple spot at the base of the petal of the Egyptian 

 cotton may appear in plants which otherwise bring only Upland char- 

 acters into expression. But the expression of the yellow color of the 

 petals of the Egyptian cotton depends very closely upon the pre- 

 dominance of Egyptian characters in other parts of the plants. 

 Egyptianlike hybrids often have wliite flowers, but Uplandlike plants 

 with yellow petals are of very rare occurrence and are usually infertile 

 or otherwise abnormal.^ 



RELATION OF DIMORPHISM TO MENDELIAN INHERITANCE. 



Dimorphic leaf characters seem to have the same intimate rela- 

 tions witii MendeUan inheritance as with the phenomenon of mutation. 

 Indeed, this might be expected from the fact that characters that 

 appear as mutations generally show Mendelian inlieritance when 

 crossed with other varieties not affected by the same mutation. 



The leaves that follow each otlier on the same stalk of a plant of 

 Deccan hemp are as definitely different as those that appear on 

 different plants in the second (perjugate) generation of crosses 

 between broad-leaved cottons and narrow-leaved "okra" varieties. 

 A cross of this kind between a narrow-leaved mutation of King and 

 a Texas varietv called Edson has been studied bv Dr. D. X. Shoe- 

 maker and found to represent an ordinary case of Mendelism. In 

 the first or conjugate generation the leaves were quite uniformly 

 intermediate, while the perjugate generation showed all three types 

 of leaves — broad-lobed, narrow-lobed, and lobes of intermediate 

 width like those of the conjugate generation. Deviations from the 

 Mendelian proportions were not greater than could reasonably be 

 ascribed to the effects of cross-fertilization. - 



Hybrids between another broad-lobed Upland variety of cotton 

 (Keenan) and an "okra" variety (Ratteree's Favorite) have been 

 made by Mr. II. A. Allard in Georgia in connection with his experi- 

 ments to determine the extent of natural crossing. Photographic 

 illustrations of the leaves of the parent varieties and the conjugate 

 hybrid are shown in Plate V, from some of Mr. Allard's specimens 

 kindly furnished for this purpose. All of the plants of the conjugate 

 generation, <S4 in number, had leaves of interme(hate form. The 

 behavior of tlie characters in the perjugate generation has not been 

 reported, but ^Ir. AHard states that a definite segregation of the 

 parental leaf forms was shown. ^ 



1 Cook, O. F. Suppressed and Inten.sifiod Characters in Cotton Hybrids, Bulletin 147, Bureau of Plant 

 Industry, U. S. Dept. of Agriculture, April, Isiu.t, p. Ki; and Hindi Cotton in K);ypt, Bulletin 210, Bureau 

 of riant Industry, U. S. Dept. of Aiiriculture, I'.ill, pp. 2.s-:«. 



2 Shoemaker, I). N. A Study of Leaf Characters in Cotton llylirids. Proceedings of ihc American 

 Breeders Association, vol. .5, p. 116. 



' Allard, H. A. rreliminary Observations concerning Natural Crossing in Cotton. American Hreeders 

 Magazine, vol. 1, 1910, p. 247. 



221 



