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CHAPTER 45 



corresponding to their positions in the cob. 

 What is observed is not all green seedlings, or 

 ail white, or all striped, or a randomly 

 distributed mixture of types; instead, groups 

 of green and of albino seedlings are found 

 (Figure 45-3). This suggests that striping 

 actually was present in the ovary also and that 

 it persisted in the cob. Other tests of this 

 strain show that the greenness or whiteness 

 of a seedling has nothing to do with the color 

 of the parental part giving rise to the pollen 

 used in the fertilization which produced the 

 seed. The only deciding factor proves to be 

 the color of the tissue giving rise to the ovary. 

 The fact that this effect is independent of 

 the pollen grain suggests that the effect is 

 not due to a nuclear gene acting differently in 

 different tissues, and by appropriate crosses 



it can be shown that none of the genes in the 

 male chromosomes is involved. In other 

 crosses this is also shown to be true for the 

 nuclear genes contributed by the mother (a 

 fact which you may have already suspected 

 from the clustering of green and of albino 

 seedlings already mentioned). We may con- 

 clude, therefore, that, in the present case, it is 

 only the nature of the plastids contained in 

 different ova which is important. 



The fact that the pollen grain is not known 

 to carry plastids, and, in the present case, has 

 no influence on the type produced after 

 fertilization, argues in favor of the view that 

 plastids are derived only from pre-existing 

 plastids, the color trait of the daughter 

 plastids being determined only by the color 

 potentiality of the parent plastid. This 



FIGURE 45-3. Groups of albino and non-albino seedlings from 

 kernels planted in rows corresponding to their positions in the cob. 



