Embryo of Cryptomeria Japonica. 439 
gametophyte. No distinct tapetum is present. Upon germination the 
nucleus of the macrospore divides and the spore enlarges. Free nuclear 
division now proceeds at a rapid rate, and the young prothallium elongates 
in the direction of the chalaza. There are now several vacuoles present, 
and the nuclei are distributed along the intervening strands of cytoplasm. 
The vacuoles enlarge and eventually flow together. The very large central 
vacuole increases enormously, and forces the cytoplasm to the wall. The 
prothallium now consists of a large central vacuole and a parietal layer of 
cytoplasm, along which the free nuclei are distributed at more or less 
regular intervals. 
As the prothallium increases in size, the parietal layer of cytoplasm 
becomes thicker and the free nuclei divide. Between the daughter-nuclei 
thus organized delicate membranes are formed. The structures thus 
formed are the first cells of the prothallium, and they are open on the 
inner side. The nuclei at this time always occupy a position at the 
periphery of the cytoplasm on the side exposed to the sap of the vacuole. 
These primary prothallial cells now elongate and grow inward towards the 
centre of the vacuole. During this growth free nuclear division proceeds, 
and numerous cross-walls are formed, but the cells nearest the vacuole are 
always open on the inner side. 
The primary prothallial cells soon become multinucleate, and by this 
inward growth eventually close up the space occupied by the sap of the 
vacuole. The membranes of these primary cells are very delicate and 
incomplete, they do not extend across the prothallium, and eventually 
take no part whatever in the formation of permanent cell-walls of the 
cellular endosperm. 
The cell-walls are formed as a result of a peculiar method of free 
cell-formation. The manner in which these walls are formed is unlike 
anything that has so far been reported for endosperm-formation. Hundreds 
of the free nuclei divide about the same time. When the daughter-nuclei 
are formed at the poles of the spindle, the kinoplasmic fibrils stretching 
between them increase in number and curve outward on all sides. No 
cell-plate is formed between the daughter-nuclei. The fibrils continue to 
increase in number, and curve out still further. This process continues 
until both daughter-nuclei are completely surrounded by a sheath of fibrils. 
The fibrils are all at the periphery of the nearly spherical structures thus 
formed. By fusion together laterally, the fibrils are gradually converted 
into a membrane which completely encloses the two nuclei. This process 
of free cell-formation goes on throughout the whole of the prothallium 
except in the region of the archegonial initials. As hundreds of these 
structures are formed they become crowded, and the walls become flat 
where they press upon one another. Through this pressure the neighbour- 
ing membranes fuse together, and this gives the appearance of ordinary 
