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CHAPTER 29 



volved. The striping effect, therefore, is 

 not due to a nuclear gene acting differently 

 in different tissues. Since the pollen grain 

 is not known to carrj plastids, and since the 

 only deciding factor proves to be the color 

 of the tissue giving rise to the ovary, it can 

 be concluded that only the nature of the 

 plastids within different ova is important in 

 determining seedling color in this case. All 

 these facts suggest that plastids are derived 

 only from pre-existing plastids and that 

 daughter plastids have the same color capaci- 

 ties as the parent plastid. 



This hypothesis is subjected to further test 

 by examining the cytoplasm of cells located 

 at the border between white and green tissue. 



I hese cells are found to contain mature 

 plastids o\' both fully green and completely 

 white types, whereas cells within a green 

 sector contain only green mature plastids. 

 and cells in a white sector contain only leuco- 

 plasts. Thus, even when the two kinds of 

 mature plastids are present in the same cell, 

 they have no influence upon each other but 

 develop according to their innate capacities. 

 If a zygote (or other cell) containing both 

 kinds of plastids produces daughter cells 

 which happen to receive only "white" or only 

 "green" plastids, these daughter cells will 

 give rise to sectors of white and of green 

 tissue. From the results presented (in addi- 

 tion to other evidence not mentioned ) it can 



FIGURE 29-2. Groups of albino and non-albino seedlings from kernels plained in rows 

 corresponding to their positions in a cob produced on a green-white striped plant. 



