56 
Sinnott. — The Morphology of the 
position, but almost immediately drops to the centre of the archegonium 
just above the large basal vacuole (Fig. 28). The three asteroids now 
disappear. The ventral canal nucleus may immediately go to pieces, may 
persist unchanged for a time (Fig. 29), or may more rarely increase to 
nearly or quite the size of the egg nucleus itself. A definite ventral canal 
cell was never observed, nor were there indications of the subsequent activity 
of the ventral canal nucleus reported by Coker. 
While the archegonia are thus reaching their mature development the 
other cells of the gametophyte are also dividing, and the embryo-sac at the 
time of fertilization has attained two-thirds or more of its final size. The 
nuclei of the endosperm cells are at first large, but after repeated cell- 
divisions decrease considerably in size. A narrow cone-shaped patch of 
tissue extending from the archegonial region to a little below the centre of 
the embryo-sac is composed of smaller and squarer cells with more proto- 
plasmic contents than the others, and with several large nuclei. The multi- 
nucleate condition extends also to a few of the other endosperm cells, but 
at this stage most of them possess only a single nucleus. 
The archegonia are now ready for fertilization and the pollen-tubes, 
which for over a month have been coming down through the nucellus, 
expand over the top of the embryo-sac and often burrow into it to some 
extent. A branch of the tube, entering and breaking through the neck of 
an archegonium, is closely followed by the two male nuclei. The functional 
one, surrounded by a layer of dense cytoplasm, is about half the size of the 
egg nucleus itself, which it immediately approaches, and to which it becomes 
closely pressed. At this time the second male nucleus and several of the 
accompanying prothallial nuclei may be observed in the upper portion of the 
archegonium (PI. V, Fig. 1). The contents of both sexual nuclei are granular, 
and the two are very similar in other details. The male, which is much 
flattened against the female, is for some time separated from it by a limiting 
membrane, but this eventually breaks down and the resulting fusion nucleus 
soon prepares to divide. 
The first mitosis takes place in the position of the egg nucleus, and the 
two small daughter nuclei, accompanied by most of the dense cytoplasm of 
the egg, migrate to the base of the archegonium and increase greatly in size. 
Each soon divides again (PI. VII, Fig. 30), as do the four which result, so that 
eight rather large free nuclei, irregularly arranged, fill the lower portion of 
the archegonium. Each of these again divides, and the resulting sixteen 
become separated from one another by the first-formed walls of the pro- 
embryo (Fig. 31). The cells are arranged in three tiers : a single binucleate 
cell at the very base, which will form the embryo, a suspensor tier of from 
seven to nine cells above this, and a rosette tier at the very top of a few 
cells which soon go to pieces. The suspensors now begin to elongate 
(PI. VIII, Fig. 32) and to push the embryo cell, protected by a thick cellulose 
