20 SPERMATOGENESIS AND FECUNDATION OF ZAMIA. 
thickened at the apex, and the micropyle through which the entire 
pollen grain must pass forms a continuous tube from the surface to 
the apex of the nucleus, a distance of about 3mm. The micropyle at 
the apex of the ovule may be seen with the unaided eye as a small 
round hole somewhat smaller than the diameter of an ordinary pin— 
about one-fourth millimeter (figs. 1 and 9). 
The nucellus at this time is about 2 mm. in diameter and pointed at 
the apex. Shortly before pollination the tissue at the apex of the 
nucellus was found to be solid entirely to the point; but just before or 
during pollination a cavity, the pollen chamber for the reception of 
the pollen, is formed in the apex by the breaking down of the tissue 
(fig. 5). The pollen grain to be effective must pass through the entire 
length of the micropyle and finally come to lie in this chamber. It is 
dificult to understand how the nonmotile pollen grains can ever reach 
the pollen chamber, which would seem to be absolutely safe from infee- 
tion by them. It is easy, however, to see how a few grains may be 
wafted by the wind into the cone, when the scales separate as above 
described, and rattle down to the axis of the cone, around which the 
apexes of the ovules are crowded. 
The passage of the pollen grain through the micropyle is evidently 
accomplished by suction. A mucilaginous, stigmatic, or micropylar 
fluid is secreted by cells of the ovule coat surrounding the micropyle, 
and this is evidently protruded in a drop from the micropyle at the 
time of pollination as a trap for the pollen. This secretion has at least 
been observed several times by the writer protruding from the open- 
ing of the micropyle at about the time of pollination, and its formation 
is thought to be of normal occurrence. This secretion later disappears, 
and a suction is probably formed by the breaking down of the cells in 
the formation of the pollen chamber which leads to the fluid, together 
with any pollen grains which have come in contact with it, being drawn 
down into the required position in the pollen chamber. The gradual 
absorption of the fluid by the cells of the nucellus bordering the pollen 
chamber would, of course, accomplish the same result. The breaking 
down of the tissue at the apex of the nucellus in the formation of the 
pollen chamber occurring about this time would seem to have some 
significance of this sort, and is believed by the writer to unquestion- 
ably be connected in some such way as above described in securing the 
passage of the pollen grains to the nucellus. In reaching the entrance 
to the micropyle of the ovule the pollen grains largely follow the trend 
of gravity. The passage of the micropyle, however, which is but 
slightly larger in diameter than the pollen grains, must be made against 
the action of gravity, and some such explanation as the above is neces- 
sary to understand how it can be accomplished. In Ginkgoand Cycas 
the pollen must pass through a similar long and narrow micropyle, and 
some such method of pollination must occur. 
