CHAPTER XVII 

 CYTOPLASMIC INHERITANCE 



In the preceding pages so much emphasis has heen 

 laid on the chromosomes as bearers of the hereditary 

 material that it may apj)ear that no very important role 

 is left to the rest of the cell. Such an impression would be 

 quite misleading; for the evidence from embryology 

 appears to show that the reactions by means of which 

 the embryo develops, and many physiological processes 

 themselves, reside at the time in the cytoplasm. Further- 

 more, there is also genetic evidence to show that certain 

 forms of inheritance are the outcome of self -perpetuating 

 bodies in the cytoplasm, most of which go under the name 

 of plastids. Recognition of plastid inheritance carries 

 with it the idea that if there are such materials in the 

 cytoplasm that are self-perpetuating they will have to 

 be taken into account in any complete theory of heredity. 



In the case of certain chlorophyll characters there is 

 excellent genetic evidence to show that a peculiar kind of 

 inheritance is due to the mode of transmission of plastids 

 in the cytoplasm. There is a race of f our-o ^clocks known 

 as Mirabilis Jalapa albomaculata, whose leaves are made 

 up of patches of green and white. Such leaves are said 

 to be checkered (Fig. 102, h). The amount of green, or of 

 white, varies on different leaves, and on such plants there 

 frequently appear leaves and entire branches that are 

 green and others that are white. The white is due to the 

 absence of green in the chlorophyll grains. Some cells 

 have only green chlorophyll bodies, and others only white, 

 still others may have the two mixed in various amounts. 



Correns has shown that if the flowers on a green 

 branch are self -fertilized they produce only green plants, 

 and these again only green plants. Flowers on wliite 



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