14 



DIMORPHIC LEAVES TN RELATION TO HEREDITY. 



ralated into the life histories of these i)huits, hke the larval stages of 

 insects. 



The joints of the stalk of the cotton plant may also be considered 



as dimorphic with reference to 

 the two kinds of branches that 

 they produce, but it is a further 

 step m hereditary specialization 

 if the joints prove to be differ- 

 entiated also by the forms of 

 leaves that subtend the two kinds 

 of branches. The external condi- 

 tions often appear to influence the 

 number of vegetative branches, 

 but it is not yet known whether 

 such changes are caused by direct 

 transformations in buds already 

 formed or are previously deter- 

 mined in the growth of the pri- 

 mary stalk. It may be that dif- 

 ferences in the forms of the leaves 

 will help to show when the char- 

 acters of the branches are deter- 

 mmed. 



In Upland varieties of cotton 

 the fruiting branches are pro- 

 duced closer to the base of the 

 plant than in the Egyptian cot- 

 ton, and the seedlings of Upland 

 cotton also begin to produce 

 lobcd leaves at earlier stages than 

 EgA'ptian seedlings. The second 

 or third leaves of Upland cotton 

 often show distinct lobes, and in 

 some varieties, such as "Willet's 

 Red Leaf," even the first leaf may 

 be luhcd. In the Egyptian cot- 

 ton, where the vegetative branches 

 are more numerous and the fruit- 

 ing branches begin farther up 

 the stalk, the seedlings usually 

 produce from five to seven entire leaves l)cl'ore the lobod leaves begin 

 to appear. In luxuriant plants the vegetative branches continue 

 farther up the stalk than the entire leaves, but under other conditions 

 the vegetative branches are less numerous. Fruiting branches have 



Fig. 3.— Leaves from adjacent inlernodes of 

 Hibiscus cannabinus, showing transition from 

 the simple to the divided form, but with the 

 lobes indicated in the simple leaf by prominent 

 angles. (Natural sire.) 



