DIMORPHIC LEAVES IN RELATION TO HEREDITY. 



17 



PARALLEL LEAF FORMS IN COTTON. 



The (liiu()r])hism of the leaves of Hibiscus cannahinus is tlie more 

 interestino; ])ecaiise a closely parallel series of leaf forms appears in 

 the cotton plant. Entire or broa(l-lo})ed leaves are found in all 

 varieties of cotton, at least during the earlv stages of growth, the 

 lobes becoming more pronounced with maturity. (Figs. 7 and 8.) 

 Narrow-leaved varieties of U})land cotton, popularly known as 

 ''olvra" cotton, show a dimorphism corresponding quite closely to 

 that of the cHmorphic-leaved Egyptian variety (fig. 9), and others 

 have a still more deeply divided, strongly digitate form, like the 

 variet}' of Hibiscus cannahinus grown in Louisiana (fig. 10). Young 

 plants of olvra cotton have, at first, entire or broad-lobed leaves like 

 the seedlings of 

 other varieties of 

 Upland cotton, but 

 whether the change 

 is gradual or abrupt 

 hasnotbeennoticed. 



Individual plants 

 with narrow-lobed 

 leaves appear occa- 

 sionallv as mutative 

 variations in broad- 

 lobed varieties. 

 Thus the narrow- 

 lobed leaf shown in 

 figure 9 represents 

 a variety called 

 ^'Park's Own," said 

 to have originated 

 as a variation of the King variety. (See fig. S.) Several other 

 mutations have been observed in experimental plantings of the King 

 cotton in Texas showing different degrees of expression of the 

 tendency to narrow lobes. 



Transitions fi'om entire to broadly lobed leaves are to be found on 

 nearly every plant of Upland cotton, though entire leaves are more 

 abundant on some varieties. Vegetative branches often have small, 

 entire leaves, like those of young seedlings, on the short basal inter- 

 nodes. The proportion of entire leaves also seems to differ in varie- 

 ties and is mfluenced by conditions of growth, humid greenhouse 

 conditions having a distinct tendency to produce more of the entire 

 leaves and to retluce the lobes of the others. 



An individual plant of Triumph cotton found in a field at San 

 Antonio, Tex., in September, 1910, showed a marked variation 

 95213°— Bui. 221—11 3 



Fig. 6. 



-Five-lobed leaf of narrow-lobed variety of Hibiscus canna- 

 hinus, grown in Louisiana. (Natural size.) 



