22 SPERMATOGENESIS AND FECUNDATION OF ZAMIA. 
responds very closely to that occurring in Cycas, Ginkgo, and the 
Conifere. The nucleus of the central cell in preparing for division 
evidently goes through changes similar to those described by Murrill 
in Zsuga canadensis; and it would be interesting to know if the same 
unique method of spindle formation occurs in Zama also. The accu- 
mulation of highly granular cytoplasm in a conspicuous mass below 
the nucleus of the central cell, as described by Murrill in Zsuqga, is 
uniformly found in stages immediately preceding division in Zama. 
The synapsis condition observed by Murrill in an early prophase of 
the division in Zsuga is also of common if not normal occurrence in 
Zamia, so that it would seem probable that the spindie formation in 
Zamia May be similar to that of Zsuga. It is interesting to observe that 
the spindle formed in this division is strikingly blunt-poled, as observed 
by Ikeno in Cycas (65) and Blackman in Pinus (16). 
Betore fecundation the canal cell breaks up and loses its identity, 
only traces of it being occasionally found at the time of fecundation. — 
After the division giving rise to the canal cell is completed, the lower 
nucleus which forms the oosphere travels from the apex of the cell 
downward toward the center and takes a position slightly below the 
middle of the cell, where it remains until fecundation takes place. It 
is usually spherical or slightly elliptical, and its contents are much less _ 
dense than the surrounding cytoplasm of the ege@ cell, with which it 
forms a marked contrast. The mature egg cell is usually elliptical or 
shghtly reniform and is about 3 mm. in length and from 1 to 1.5 mm. 
in width. The nucleus is very large, being about 553 4 long and 467 mu 
in diameter. It is plainly visible to the unaided eye in stained sections 
and it is hard to realize ‘on looking through a section held up to the 
light that one is viewing the egg cell and its nucleus without even the 
use of a hand lens. 
In the development of the prothallus a circular depression known as 
the archegonial chamber (prothallial or endosperm cavity) is formed 
in the upper part of the prothallus immediately above the archegonia 
and beneath the apex of the nucellus (fig. 9). 
This cavity is usually about 2 millimeters in diameter and a milli- 
meter deep. It is into this cavity that the pollen tubes later grow 
and discharge their spermatozoids. The openings to the four arche- 
gonia can be seen easily in the bottom of the cavity, the two neck 
cells being turgid, hyaline, and quite distinct in appearance from the 
surrounding cells of the prothallus. They protrude above the general 
surface and appear to be under considerable tension. 
DEVELOPMENT OF THE POLLEN TUBE AND PROTHALLUS. 
GERMINATION OF POLLEN AND GROWTH OF PROTHALLUS. 
Very shortly after the pollen grains have been drawn down into the 
pollen chamber of the nucellus they germinate, the tube, which at first 
is about the diameter of the pollen grain or slightly less, bursting out 
