638 Kershaw .- — Structure and Development of the 
very shallow compared with that in ovules of Cycas and Dioon (Text-fig. 13). 
The prothallus is surrounded by the megaspore membrane, which adheres 
closely to the nucellar tissue rather than to the prothallus. This membrane 
is still very thin, showing little increase in thickness, if any, from that of the 
younger ovule. The prothallus tissue consists mainly of large cells with 
two or three rows of smaller cells at the exterior. In the neighbourhood 
of the archegonia also the cells are small. They have thin walls and nuclei 
and no visible stored food material. In the specimens investigated the 
protoplasm had shrunk considerably from the walls. The archegonium is 
about 1*7 mm. long and surrounded by a conspicuous jacket layer. It has 
a pair of arched neck cells above, which are evidently formed by a transverse 
division of a single cell (Fig. 17, PI. LXI). The contents of the archegonium 
consist of foam-like vacuolated protoplasm, with a single nucleus 0-03 mm. in 
diameter at the apex (Fig. 1 8, PI. LXI). The nucleus has an irregular outline 
and contains numerous masses of chromatin, and various sized granules of 
a staining substance are scattered around the nucleus in the protoplasm. 
In Fig. 1 8, PI. LXI, two large masses of this substance are seen. It seems 
very probable that these granules are similar to those described by Ikeno 1 as 
proteid granules. The central cell of the archegonium is surrounded by 
a thick ‘egg membrane’ in which there are pits of various sizes (Fig. 19, 
PI. LXI). Through the pits haustoria-like processes of the ‘ egg ’ protrude to- 
wards the surrounding cells of the jacket layer, the protoplasm of which is very 
dense and often contains, in addition to the large nucleus, several granules of 
a substance which stained like chromatin. It has been asserted by several 
investigators that a thin wall closes the pits of the thick egg membrane. 
No such closing membrane to the pit can be seen in these ovules with the 
highest magnification. The preservation of the material may account for 
this ; or it may be, as Chamberlain 1 suggested, that the pit membrane 
which probably exists in the younger stages is ruptured by the haustoria as 
they grow out towards the jacket cells. 
(c) Abnormal Ovules. 
The two stages of abnormal ovules were of use in showing intermediate 
steps in development, especially as regards the pollen-chamber, between 
those already dealt with. The main features of these ovules will be 
described before discussing the development and morphology of the pollen- 
chamber in Cycads. 
The younger ovules were about 4 mm. long. A vertical section of one 
of them is represented in outline in Text-fig. 14. In all ovules of this age 
the pollen-chamber was completely formed, and many of them contained 
a prothallus with several archegonia ; but in all cases it had shrunk, some- 
times considerably, from the megaspore membrane. Some of the ovules 
1 Ikeno : Cycas rcvoluta. Jahrb. wissensch. Bot., vol. xxxii, 1898. 
