54 SPERMATOGENESIS AND FECUNDATION OF ZAMIA. 
correct, and that Hirase and Fujii probably erred in figuring a mother 
cel] in Ginkgo, inside of which the spermatozoids are differentiated. It 
is important to note furthermore that in Fuju’s figures (40, figs. 2 and 
5), the drawings, when critically examined, do not show the differen- 
tiation of the spermatozoids inside of the mother cell, as no wall is 
shown separating the two spermatozoids. When the central cell 
divides into two cells they are separated by a definite membrane. If, 
then, each one of these mother cells develops a spermatozoid inter- 
nally, this separating membrane should remain between the develop- 
ing spermatozoids, but this is evidently not the case, judging from the 
figures. Fujii’s figure 2 seems to illustrate exactly the same appear- 
ance as that described above as occurring in Zamza when the sperma- 
tozoids pull away from each other and round up so that they occupy 
less space, and have their original location marked by the surrounding 
plasma membrane of the pollen tube. The writer believes that it may 
be safely concluded that Ginkgo corresponds with Zamia and Cycas in 
the metamorphosis of the entire cell, and, as stated above, believes 
that this method of differentiation is in harmony with what is found 
in Marsilia, and probably in other ferns and lower plants. 
MOVEMENT OF SPERMATOZOIDS. 
For purposes of microscopic study the pollen tubes were cut off 
some distance above the prothallus and placed on ordinary microscopic 
slides, hollow-ground slides, or in glass chambers in solutions of cane 
sugar. In the beginning of the studies water was used, but this proved 
very unsatisfactory, as the spermatozoids soon died and burst, evidently 
from the difference in density of water and the contents of the cells. 
Solutions of cane sugar of several strengths were tried and a solution 
of about 10 per cent gave in general the best results. By the use of 
this solution the spermatozoids were kept living and moving for a 
considerable time, making it possible to study them quite carefully in 
a living condition. If they are transferred to the sugar solution with- 
out injury they usually continue to move from thirty to sixty minutes 
and one instance was recorded where motion continued for two hours 
and forty-four minutes. The feat of cutting off the pollen tubes 
which hang down from the apex of the nucellus, as shown in figure 51, 
is by no means as difficult as might be supposed, judging from the size 
of pollen tubes and sperm cells in plants ordinarily. Here the pollen 
tubes and spermatozoids are so large that they are plainly visible to 
the unaided eye and can be easily handled under an ordinary dissecting 
lens. In the manipulation the ovaries are cut open and the upper 
part of the membraneous nucellus with the pollen tubes removed.,. The 
nucellus can then be inverted over the first finger of the left hand and 
held in place by the thumb and second finger. Held in this way the 
tubes protrude prominently and can be easily cut off with asharp 
