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 
Fia. 113.—Transition from one form of leaf to another on the same branch in (a) Euca- 
lyptus globulus (b) Hedera heliz. 
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- 
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