SPERMATOPHYTES 
201 
a Cuban cycad (Microcycas) recently 
studied, as many as sixteen mother 
cells and sperms have been found in a 
single pollen tube. Within each mother 
cell a large, spirally grooved, multi- 
ciliate sperm is formed (figs. 453, 454), 
which is discharged and swims freely 
(figs. 455, 456). The blepharoplast 
has received its name from the fact 
that it develops the cilia. The dis- 
covery of these swimming sperms of 
Cycadales was quite unexpected, since 
it had been supposed that all seed plants 
had abandoned swimming sperms ; but 
the discovery served to emphasize the 
fern connections of the cycads. 
Fertilization. The pollen tube pene- 
trates the tissue of the nucellus in vari- 
ous directions, often branching, and 
always functioning as an absorptive 
structure (haustorium). Finally it col- 
lapses, and the tube nucleus may return 
to the grain end of the tube. In the 
meantime the tissue of the nucellus 
lying between the pollen chamber and 
the archegonial chamber has broken 
down, and the two chambers become 
continuous. Then the sperms are dis- 
charged into the archegonial chamber, 
and finding their way into the arche- 
gonium fertilize the egg. It is evi- 
dent that the pollen tube in these 
primitive seed plants is not a means of 
FIG. 459. Differentiation of proembryo of 
Zamia by elongation of cells of suspensor region; 
unelongated cells above suspensor forming the 
"rosette"; apical group of small tneristematic 
cells (note spindles) to form the embryo. After 
COULTEK and CHAMBERLAIN. 
469 
