12 



DIMORPHIC LEAVES IN RELATION TO HEREDITY. 



varieties of cotton representiniii; two corresponding types of leaves. 

 The hemp pLants with the two kinds of leaves represent a segrega- 

 tion of characters among the internode members of the same plant. 

 The leaves of the upper part of the stem are all deeply lobed, while 

 those of the lower part are without lobes. The transition is usually 

 quite abrupt, though the leaves that are close to the transition are 

 often slighth" different from others of the same class. A premonition 

 of the change may be found in the larger margmal teeth of the last 

 of the undivided leaves (fig. 2), or the last simple leaf may have a 

 prominent angle on one or both sides (fig. 3). A more definitely 

 intermediate condition aj^pears when a leaf is divided on one side 



Fig. 1 .—Growing tips of stalks of Hibiscus mnnabinus, shomng changes from 

 simple to lobed leaves. (Natural size.) 



but not on the other. (See PI. II.) In such cases there is usually 

 a ver}^ pronounced difference between the two sides of the leaf, so 

 that the change from the enth'e to the lobed condition is still quite 

 abrupt in comparison with the very gradual changes shown in many 

 ])lants in passing from the large basal or radical leaves to those of the 

 upper i)art of the stalk. 



Specimens to illustrate the abrui)t nature of the transition from 

 the entire to the lobed form of leaf (PI. I) were taken quite at 

 random, excejit for the necessity of seekmg plants that had unin- 

 jured leaves at the nodes where the transition took place. Many of 



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