32 SPERMATOGENESIS AND FECUNDATION OF ZAMIA. 
from them for a considerable time. In this latter feature they seem 
to be considerably different from Zamia, where the radiations are 
visible and conspicuous in the youngest stage which can be detected. 
In Ginkgo, also, as shown by the writer (124) and Hirase (62), the 
blepharoplasts appear in the central cell just after its formation, arising 
in the cytoplasm near the nuclear membrane. It is probable that 
Lamia, Cycas,and Ginkgo, agree in their main features, the absence of. 
radiations in Cycas being probably due to the method of preparation. 
In this stage of development in Zama the central cell is still almost 
spherical, being flattened at the point of attachment with the stalk 
cell, as is shown in figure 19. Here the central cell is only about 36 yu 
in diameter, while the nucleus is about 183 yu, the nucleolus 44 y, 
and the blepharoplasts 1 4 in diameter. The first prothallial cell is 
shown here very plainly, pushing up into the stalk cell, extending fully 
two-thirds of the distance through it. The nucleus of the prothallial 
cell and that of the stalk cell are about the same size, the latter nucleus 
having increased in size since the stage illustrated in figure 18, and 
become somewhat compressed and lenticular from pressure. The 
pollen tube at this stage has reached a length of about 1 mm., and is 
at most places in the tissue from 40 to 50 “in diameter, though this 
varies considerably. The protoplasm forms an open foam structure 
with large vacuoles, about the same as illustrated in figure 19. Starch 
grains have already become abundant in the tube, but are not so large 
or so numerous as in later stages. In the section figured no starch 
grains were visible in the stalk cell or prothallial cell, although in 
some instances they are formed in a still earlier stage. 
The first indication of differentiation in the blepharoplast, as it 
increases in size, is the formation of an outer membrane or wall 
(fig. 25). By this time the blepharoplasts have moved somewhat 
farther away from the nucleus and the kinoplasmic radiations have 
become much longer, more prominent, and apparently more numerous. 
The central cell has also increased in size, as well as the entire pro- 
thallus. Up to this time the central cell has been nearly spherical 
in outline, and the blepharoplasts, so near as the writer has been able 
to observe, did not seem to occupy any definite position in reference 
to the attachment of the stalk cell. As the apparatus increases in size 
the central cell elongates and becomes elliptical or oblong, its major 
axis corresponding to the longitudinal axis of the pollen tube (fig. 20). 
The blepharoplasts during this development take up a position on 
opposite sides of the nucleus almost exactly on the major axis of the 
cell. In almost all of the cells in this stage of development the bleph- 
aroplasts occupy this position. In a number of instances, however, 
they have been observed to remain much closer together, and in some 
instances never assume a position opposite each other. In this early 
stage of development the central cell presents a beautiful reticular 
