| 
WEATHERWAX: GAMETOGENESIS IN ZEA Mays 79 
The path of the pollen tube on reaching the ovary has never 
been satisfactorily explained. True (20, p. 217) quotes Hackel 
(11) as saying that the outer integument acts as a conducting 
tissue. Guignard (10, p. 43) says that the tube enters the ovary 
by way of the stylar canal. My preparations have not given 
conclusive results, but .they do not tend to substantiate these 
opinions. The pollen tube seems to grow downward from the 
base of the style until it reaches the inner epidermis of the wall 
of the ovary (TExT FIG. 2). Remnants of it can be traced just 
below the epidermis to a point near the micropyle, where it enters 
the ovarian cavity. After following a very crooked course here, 
it finally enters the micropyle, forces its way between the cells of 
the parietal tissue, and enters the embryo sac (FIG. 16). 
FECUNDATION 
The contents of the pollen tube may be emptied between the 
cells of the egg apparatus or into any one of them; but it is usually 
emptied into a synergid. The membrane of the other synergid 
often seems to break at about the same time, emptying its contents 
into the cavity of the endosperm cell. The tube nucleus is soon 
lost to view, if it was visible at all; and, because of their extremely 
diminutive size, it is very difficult to follow the sperms beyond 
this point. The cytoplasm of the area to be examined is very 
dense and is filled with numerous globules of various sizes and 
shapes (FIGS. 13, 16), produced, no doubt, by the mixing of the 
cell contents brought together by the entrance of the pollen tube. 
The disorganizing synergids give rise to cytoplasmic differentia- 
tions that are especially confusing. Material fixed with reagents 
containing osmic acid presents almost hopeless complications; 
but, with chromo-acetic acid as a fixing agent, followed by Flem- 
ming’s triple stain, the sperm nuclei can be identified. 
In several preparations a small red object, which is like a 
sperm nucleus in size, shape, and granular appearance, has been 
seen sticking to the egg nucleus (Fic. 17); and a similar body has, 
in a number of instances, been seen attached to one (Fic. 18) or 
both (Fic. 19) of the polar nuclei, which were in the process of 
fusion. No fusing polar nuclei have been seen without this 
sperm-like body. On this basis, then, it seems certain that the 
so-called “‘double fecundation”’ takes place in maize. 
