1906] CHAMBERLAIN—OVULE OF DIOON 345 
all to ten. Several ovules at the period of fertilization showed no 
archegonial chamber and no trace of archegonia. Ten archegonia 
were observed in only a single instance, which was also exceptional in 
having two archegonial chambers. A single archegonium with a small 
archegonial chamber was observed in a few cases. Usually there are 
three, four, or five archegonia, with four as the most frequent number. 
An archegonium initial, which can be seen- early in November, 
becomes distinguishable by its slightly greater size (figs. 22, 23). 
The division into a neck cell and central cell takes place early, prob- 
ably in November (fig. 24). The neck cell divides almost immediately, 
forming the two-celled neck which is a constant feature in all cycads 
yet investigated. All December ovules not only showed the neck, 
but the neck had already divided into its two characteristic cells 
(jig. 25). 
The central cell enlarges very rapidly, its scanty protoplasm form- 
ing a delicate layer pressed against the wall by the single large sap 
vacuole (jigs. 24, 25). Even at the stage shown in fig. 24, the cells 
bordering upon the central cell are rather regularly arranged, and in 
fig. 25 there seems to be a definite jacket. While this layer functions 
more or less in the nutrition of the central cell, the real archegonial 
jacket with its characteristic cell contents is formed later by both 
periclinal and anticlinal divisions in the jacket-like layer of fig. 25. 
The differentiation of the jacket is not so rapid at the apex of the cen- 
tral cell as at the sides and base. As soon as the jacket begins to be dif- 
ferentiated from the neighboring cells, the cytoplasm of the central cell 
increases rapidly, and soon the space which had been occupied by the 
single large vacuole is filled. The rapidly increasing cytoplasm shows 
a beautiful foam structure (fig.26). At this stage there is no reticulum 
or even any fibers. - The vacuoles of the central cell are much smaller 
at the apex and at its periphery than nearer the center. The walls of 
these vacuoles are themselves vacuoles, and there is a perfect grada- 
tion, so far as size and appearance is concerned, from the large vacuole 
near the center to the smallest vacuoles of the thin plates of cytoplasm 
Which form the walls of the large vacuoles. Some of the walls of 
the larger vacuoles are shown in surface view in fig. 26, though 
Most of the walls show only the edges, as in case of cell walls. The 
smallest of the vacuoles are small enough to come within BUTSCHLI’s 
