B. P. I.— C75. 



DIMORPHIC LEAVES OF COTTON AND ALLIED 

 PLANTS IN RELATION TO HEREDITY. 



INTRODTTCTION. 



Parallel series of variations in the forms of the leaves can be 

 traced through numerous species of cotton and also in other genera 

 of Malvaceae, such as Hibiscus, Abelmoschus, and Ingenhousia. The 

 parallel variations appear as characters of different cultivated varie- 

 ties and are also represented by dimorphic specializations of leaf 

 forms in difl'erent parts of the same plant. 



Though this class of variations has received little attention hitherto, 

 the facts are of interest in relation to general questions of heredity 

 and to tlie practical problems of breeding superior varieties and 

 maintamiiig their uniformity by selection. Recognition of dmior- 

 phism of the leaves and branches in cotton and related plants enlarges 

 the range of characters that may be used m distinguishing varieties 

 and in determining the influence of environment upon the expression 

 of characters. 



The cotton plant affords unusually good opportunities for the 

 study of environmental modifications, but it is essential that the 

 characters and habits of the various cultivated forms be well known 

 if the differences of behavior in different conditions are to be cor- 

 rectly understood. Studies of environmental differences or of corre- 

 lations of characters that do not take into account the normal diver- 

 sity in the structure of the different parts of the plant may give very 

 misleading results. 



Though different kinds of leaves or branches represent very definite 

 facts of heredity, yet the expression of such characters can be influ- 

 enced by external conditions. Thus it has been found that new con- 

 ditions may seriously disturb the expression of characters in the cotton 

 plant, even to the extent of a complete suppression of the fruiting 

 branches, so that the plants remam completely sterile, although 

 showing a high degree of vegetative vigor. The behavior of such 

 plants may be compared with that of sterile hybrids. In both cases 

 there is a failure to bring the full series of normal characters into 

 expression.^ 



1 Cook, O. F. Dimorphic Branches in Tropical Crop Plants: Cotton, CoiTee, Cacao, the Central Ameri- 

 can Rubber Tree, and the Banana. Bulletin 198, Bureau of Plant Industry, U. S. Dept. of Agriculture, 

 1911, pp. 18-27. 



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