18 SPERMATOGENESIS AND FECUNDATION OF ZAMIA. 
central cell when it divides gives rise to the spermatids, which become, : 
metamorphosed directly into spermatozoids. The entire apparatus, 
including the stalk cell and central cell (Kérperzelle or generative 
cell) is spoken of throughout as the male prothallus, or simply pro- 
thallus where it is not necessary to distinguish more closely. The 
nomenclature here given corresponds with that used by Shaw in 
Marsilia (102). 
In the case of Ginkgo, judging from Strasburger’ sand Hirase’s fig- 
ures, the walls of the prothalhal cells cut off extend comparatively 
straight across the pollen grain, in each cell the new wall as formed 
being attached to that of the pollen grain. In Zama quite a differ- 
ent form is found. Here the cells arch out into the tube cell of the 
pollen grain (fig. 11). In none of these cells is a cellulose wall laid 
down, there being nothing but a plasma membrane or hautschicht 
formed. The first prothallial cell is shaped like a plano-convex lens 
and arches out into the second prothallial cell. In the mature pollen 
grains it can not be determined whether the plasma membrane formed — 
in cutting off this cell is attached at the sides to the plasma membrane 
of the tube cell, as must be the case if only two prothallial cells are 
formed, or to that of a third resorbed prothallial cell. In some cases 
of germinating pollen grains where the prothallial apparatus has. 
developed considerably and where remnants of a resorbed third pro- 
thallial cell can be observed, the attachment would seem to be to the 
plasma membrane of this cell (figs. 13 and 14). This would also be 
indicated by Juranyi’s figures of Ceratozamia (72, Taf. 33, figs. 8-11). 
The second prothallial cell is attached to the first prothallial cell and 
arches out into the tube cell. Its membrane is connected only with 
that of the first prothallial cell. This cell, while the most important 
and ultimately much the largest, is in the mature pollen grain consid- 
erably smaller than the first prothallial cell. The protoplasm of the 
prothallial cells is densely granular and the nuclei, which nearly fill the 
cells, are difficult to distinguish. The nucleus of the tube cell is much 
larger than the nuclei of either of the prothallial cells and is situated 
at the apex of the prothallus. eee 
The mature pollen grain of Cycas revoluta, as shown by Ikeno (70, 
Pl. VILL, fig. 13), would seem to be considerably different from Zama, 
in that the cell membrane of the prothallial cell extends straight across 
the grain, as figured by Strasburger and Hirase in Ginkgo, instead of 
arching out into the tube cell as in Zamia. The structure described 
by the writer in Zama is the same as that described by Juranyi (72) 
and Guignard (45) as occurring in Jacrozamia. 
Pollination in both of the species of Zamza studied apparently takes 
place in the latter part of December and first of January, and is accom- 
plished mainly through the agency of the wind. The pollen is pro- 
duced in great abundance and is light and easily carried. The scales 
