MUTATIONS 



275 



of the process of mitosis (see p. 60). It has been shown by Babcock 

 and Lloyd that no special significance should be attached to the occur- 

 rence of a ratio which, under the laws of simple sampling, could not occur 

 oftener than once in 1,155,000,000,000,000 times, especially in view 

 of the fact that these two varieties are presumably complex hybrids, and 

 the persistency and deciduousness of the calyx lobes were variable in 

 the parents. Hence to use the term somatic segregation in attempting 

 to explain phenomena such as these is not only unwarranted but posi- 

 tively misleading. 



The multifarious manifestations of dimorphism in plants are, in 

 general, the result of alternative expression of inherited characters rather 



FIG. 113. Transition from one form of leaf to another on the same branch in (a) Euca- 

 lyptus globulus (b) Hedera helix. 



than alternative transmission of different factors. There are, to be sure, 

 various cases of dimorphism within species, such as the different forms 

 of flowers described by Darwin or the zygomorphic and peloric snap- 

 dragon flowers, which usually do not appear together on the same 

 plant and which exhibit alternative inheritance when crossed. But there 

 are many species which bear different forms of branches, leaves, flowers 

 or other organs on the same plant. Cook has described dimorphic 

 branches in cotton, coffee, cacao, the Central American rubber tree and 

 the banana, also dimorphic leaves in cotton, hibiscus, okra and allied 

 genera. The open and cleistogamous flowers of the violet make a familiar 

 example of dimorphism in the same plant. In all these cases it appears 

 that the individual plant contains all the factors conditioning the expres- 



