152 Plant Genetics 



the fusion nucleus and male nucleus divide separately 

 to form endosperm. Webber concludes that in this 

 last case there will be very much white and very little 

 red in the mature grain; for the fusion of the polars 

 to form the fusion nucleus has resulted in the usual 

 growth stimulus that is evident in all fusions. In the 

 previous case in which all three divided separately, if 

 more white than red develops, it is simply because there 

 are two female polars (white-producing) to one male 

 gamete (red-producing). In the latter case, however, 

 the fusion of the two female polars stimulates them to 

 more rapid division, so that they greatly preponderate 

 over the single unstimulated male gamete, the result 

 being that much white and Uttle red appears in the 

 mature grain. 



The appearance of red and white blotches rather than 

 a more regular distribution of colors is explained by the 

 usual method of endosperm formation. Endosperm 

 formation begins with free nuclear division, the resulting 

 nuclei being free in the cytoplasm of the sac. The 

 cell walls, which limit them, are not formed for some 

 time; sometimes not until all the nuclei have been 

 formed. Before a large number of free nuclei have 

 appeared they move from the central region of the sac 

 and usually become placed near the wall, where free 

 nuclear division continues. When walls begin to appear, 

 separating the nuclei, wall formation begins at the 

 periphery of the sac and extends toward the center, 

 in what is called centripetal growth. This program, 

 which is common in seed plants and is known to occur 

 in wheat, is doubtless the program in corn. If then the 

 second male gamete fails to unite with the fusion nucleus 



