RELATION OF DIMORPHISM TO INHERITANCE. 37 



As the illustrations of the loaves of Hibiscus cannahinus haveshowTi, 

 the transition from the entire to the tlivided leaves is not equally 

 abrupt on all |)lants, hut neither is it usual for the two types repre- 

 senteil in a Menilelian ])roo;eny to have the contrasted characters 

 equally expressed in all individuals. Narrow-leaved mutations from 

 the broad-leaved varieties of cotton are not all equally narrow leaved, 

 nor do the narrow-leaved members of a series of perjugate hybrids 

 all have leaves with lobes of the same width. The range of varia- 

 tion in the perjugate generation is not only vastly greater in total 

 extent than in the first or conjugate generation, but also seems to be 

 greater among the perjugate plants that represent the narrow-leaved 

 group. It is to be expected, however, that these general differences 

 in the range of expression will also be found to vary in difl'erent 

 hybrid combinations, just as there may be differences in the abrupt- 

 ness of the transition from one type of leaves to the other in different 

 varieties. 



;i_In progenies raised from the seed of okra-leaved mutations grown 

 in fields of the parent variety and subject to natural crossing, both 

 broad and narrow leaves appeared, rather than leaves of intermediate 

 form. Thus the progeny of a narrow-leaved mutation grown by 

 Dr. Shoemaker at Waco, Tex., in 1906, showed the narrow-lobed 

 type of leaves in only about a quarter of the plants, the remainder 

 appearing to be normal broad-leaved examples of the King variety. 

 The progeny of another okra-leaved mutation of the King, selected 

 at San Antonio, Tex., in 1907 and tested at the same place in 1908, 

 showed 20 plants out of 34 with broad leaves, 13 plants with leaves 

 like the parent mutation, and 1 plant with a more extreme expression 

 of the narrow-lobed tendency, as though another mutative step had 

 been taken. ^ 



The second type of dimorphic leaves in cotton, that connected 

 with the dimorphism of the branches, is similarly related with Men- 

 delian inheritance as well as with mutative variation. Branch char- 

 acters show Mendeloid expression of characters in hybrids, as well as 

 leaf characters. Crosses between cluster and noncluster cottons of 

 the Upland type do not manifest the cluster habit in the conjugate 

 generation, but the cluster character returns to delmite expression in 

 the perjugate generation. - 



The interest of the dimorphic leaves of Hibiscus cannahinus in 

 relation to Mendelism is to show that a change of characters quite 

 as extensive and abrupt as those that characterize ISIendelian hybrids 



1 Cook, O. F. Local Adjustment of Cotton Varieties. Bulletin 159, Bureau of Plant Industry, U. S. 

 Dept. of Agriculture, September, 1909. 



2 Cook, O. F. Suppressed and Intensified Characters in Cotton Hybrids. Bulletin 147, Bureau of Plant 

 Industry, U. S. Dept. of Agriculture, April 7, 1909, pp. 22-23. 



221 



