130 : BOTANICAL GAZETTE [ AUGUSI1 
of this nutriment before cell walls are formed. They have the 
appearance of streams bearing granules. The final and penul- 
timate divisions of the nuclei are distinguished by the appearance 
of nuclear plates and spindles of quite different appearance, 
which result in the formation of definite cells with cell walls, 
each containing a single nucleus ( figs. 26-28). At this stage, 
each nucleus is so surrounded by a mass of proteid as to be 
completely obscured. The only cells not thus gorged are a 
limited number which lie in the upper layer nearest the apex, 
beneath the trefoil-shaped cleft in the exospore (fig. 54). By 
continual multiplication they form a prothallial cushion, which 
widens the breach and bulges through. These cells are much 
smaller than those filled with the food supply. There may be 
from three to five layers inthis cushion. There is no diaphragm ) 
between the region designated the prothallial cushion and the | 
mass of storage cells underlying it. 
ARCHEGONIA.—A few cells in the prothallial cushion soon 
become conspicuous by reason of their large nuclei. Each 
divides by two periclinal walls, forming a tier of three cells. 
The uppermost of these divides by two anticlinal walls at right 
angles to each other into four cells. These again, by periclinals, 
form.the four cover and the four neck cells. The middle one of 
the original tier does not divide and becomes directly the single 
neck canal cell. The lowermost divides into the egg and the 
ventral canal cell ( figs. 29-32). A suggestive irregularity 
sometimes occurs in the last mentioned division. The central 
cell, that is, the lowermost cell of the original tier, may divide 
in such fashion that the egg and its sister, the ventral canal cell, 
may lie side by side in the venter of the archegonium, instead 
of in the normal fashion of ventral canal cell above the egg 
(fig. 32). The cover cells project very little from the surface x 
of the prothallium. Thus the archegonia are imbedded in the a 
surrounding tissue, whose cells in immediate contact with the 
egg and the ventral canal cell become more or less modified in 
form. The neck canal cell pushes up like a wedge, spreads 
apart the four neck cells, and dissolves. The ventral canal cell 
