26o Journal of Agricultural Research voi. xviii. no. 5 



in this experiment, although approximately 50 observations were made. 

 This fact was also observed by Weatherwax {16) in the varieties of corn 

 studied by him, so it seems to be the rule that all four megaspores func- 

 tion. In wheat (Triticuvi vulgare), however, Koernicke (8) and Jensen 

 (6) report that only one megaspore functions. The same has been 

 observed by Cannon (j) for wild oats (Avena fatua). 



The megaspore mother cell increases in size until it becomes about 

 twice as broad and from four to five times as long as the vegetative 

 cells of the ovule (PI. 26, A, B). The developing embryo sac remains 

 approximately the same size as the megaspore mother cell until the 

 eight -cells are formed. At that time it has elongated but slightly while 

 its breadth has increased to two or three times that of the megaspore 

 mother cell (PI. 27, B). ' The two polar nuclei migrate and come in 

 contact with each other a short distance above the egg but do not fuse 

 before fertilization takes place (Pi. 27, B, C). In scores of cases where 

 pollination had been prevented the two polar nuclei were observed 

 standing apart a week or more after the embryo sacs were ready for 

 fertilization. 



MATURE) EMBRYO SAC 



• 



When the embryo sac is mature, it is approximately four times as 

 long and about twice as wide as when it first reaches the 8-celled stage. 

 It reaches its maximum size about the time the silk emerges from the 

 husk. The antipodals begin to divide almost immediately after the 8 cells 

 are formed, so that one very rarely finds an embryo sac that shows only 8 

 cells. The antipodals increase in number, apparently by indirect cell 

 division, until they number from 24 to 36 cells at the time of anthesis. 

 These cells often have indistinct walls, and frequently there are two nuclei 

 to each cell. These cells are closely crowded together and give the 

 appearance of a rather definite tissue (PI. 28, ant). This behavior of the 

 antipodals is characteristic of the grasses and has been noted by numer- 

 ous investigators since the time of Hofmeister (5). Golinsld (j) in his 

 work with the stamens and pistil of wheat studied the antipodals with 

 especial care in order to determine whether they played any part in the 

 formation of the endosperm and established the fact that these cells 

 remain intact until they are crowded out by the growing endosperm 

 (PL 32, B). 



The egg increases in size until its width is almost half that of the 

 embryo sac. It is decidedly balloon-shaped and becomes aveolar in 

 appearance. The synergids are more or less lunar-shaped and are 

 considerably longer than the egg. They have dense cell contents and 

 take the stain much deeper than the egg. (PI. 28, e, sy). The nuclei 

 of the synergids may disintegrate before fertilization or may remain 

 clear and distinct until it has taken place. In most cases the synergids 

 do not remain long intact after the egg is ready for fertiUzation. Where 



