GYMNOSPERMS. 149 
Ginkgo, the spermatozoid of Cycas, as has been pointed out for the 
fern, is a transformation of the entire mother-cell. 
The development of the spermatozoid in both Grzkgo and Zama 
closely resembles that in Cycas. That in Zaméa differs, however, 
according to Webber, in certain important details, and because of this 
fact the process in Zamda will be given also in some detail. Webber 
investigated two species growing in Florida—Zamia floridiana and 
Z. pumila. 
As a rule the mature microspore of Zamda consists of the tube cell 
and two prothallial cells (Fig. 60, A). Only in exceptional cases were 
evidences of a third cell observed, but if three prothallial cells are 
formed in the development of the pollen spore as is claimed for Cycas, 
the first is generally absorbed before the spore is mature, leaving only 
a trace in the form of a dark line. The two prothallial cells are pro- 
vided with only a plasma membrane. The first prothallial cell is shaped 
like a plano-convex lens and arches out into the second prothallial 
cell, The second prothallial cell is attached to the first and arches out 
into the tube cell (Fig. 60, A, B). This is especially marked during 
the growth of the pollen tube. The nucleus of the tube cell is larger 
than those of the prothallial cells, and of the latter the nucleus of the 
first is larger than that of the second. Very soon in the growth of the 
pollen tube the second or antheridial cell, together with its nucleus, 
greatly exceeds the first. 
The process of pollination, which occurs in Florida in January, 
brings the pollén grains into the pollen chamber, a cavity in the apex 
of the nucellus, formed by the disorganization of the tissue of the 
latter. Webber (’or) states that the passage of the pollen grain 
through the micropyle is evidently accomplished by suction. 
A somewhat mucilaginous fluid is secreted by the cells which sur- 
round the micropyle, and a drop of this fluid is probably protruded 
at the time of pollination. The fluid disappears later, and during the 
formation of the pollen chamber a suction is formed by the breaking 
down of the cells in its formation, so that the fluid, together with 
the pollen grains that may be held in it, is brought down into the 
pollen chamber. 
In a short time after the pollen grains have been brought into the 
pollen chamber they germinate, the tube bursting out of the exine of 
the grain at a point opposite the prothallial cells (Fig. 60, B). No 
matter what the position of the grain may be, the tube always pene- 
trates the tissue.of the nucellus adjacent to the chamber. The tube in 
Zamia does not branch before entering the nucellar tissue, and only 
