. Genetics in relation to agriculture. Livestock; Heredity; Variation (Biology); Plant breeding. 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 atte
. Genetics in relation to agriculture. Livestock; Heredity; Variation (Biology); Plant breeding. 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 (h) Hcdera 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- Digitized by Microsoft®. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these ill
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