GNETALES— GNETUM 421 



ning near the tube nucleus. By this time, a definite body cell has 

 been organized about the body nucleus, and, with the tube nucleus, 

 it passes into the pollen tube, while the stalk nucleus remains be- 

 hind. Pearson does not regard this nucleus as a stalk nucleus, but 

 as prothallial. Some of the pollen grains reach the nucellus directly 

 and germinate there. Germination at a distance from the nucellus 

 adds another angiosperm feature to the growing list. 



The nucleus of the body cell divides as the pollen tube grows 

 down into the nucellus, but no wall is formed between the two nu- 

 clei. They may differ somewhat in size, and Thompson^'^" thinks it 

 probable that only the larger one functions, and that the other dis- 

 organizes. 



THE FEMALE GAMETOPHYTE 



The megaspore is the first cell of the female gametophyte. As in 

 all other gymnosperms, its germination begins with a series of free 

 nuclear divisions, but, unlike all other gymnosperms, the gameto- 

 phyte — at least the micropylar end of it — remains in the free nu- 

 clear stage, up to the time of fertilization (fig. 393). There has been 

 some difference of opinion regarding the lower part of the gameto- 

 phyte. LoTSY^^^ described a tissue which he interpreted as homolo- 

 gous with the antipodal cells of angiosperms, only more extensive. 

 Coulter'''^ thought that Lotsy"' had mistaken the extensive 

 nutritive tissue at the base of the gametophyte, undoubtedly a 

 sporophytic tissue, for a part of the gametophyte itself. A study of 

 the figures and descriptions of both authors, and also the later work 

 of Thompson,^-''' together with the re-examination of Coulter's 

 material, make it certain that there is a considerable amount of 

 cellular tissue at the base of the gametophyte and definitely within 

 the megaspore membrane. Thompson shows very clearly the origin 

 of this tissue, which develops from the free nuclear condition, just 

 as in Welwitschia (fig. 394). The first walls are formed irregularly, 

 without any connection with the mitotic figures, and inclose several 

 nuclei in each cell. The nuclei, which are rather small, then begin to 

 fuse, and the cells become uninucleate, with one large nucleus in each 

 cell. Consequently, the tissue corresponds to the antipodal cells of 

 angiosperms, which, in many cases, are quite numerous before 



