EMBRYO-SAC OF GYMNADENIA CONOPSEA. 
13 
expose its one or two rudimentary archegonia. These con- 
sist of an oosphere, surmounted by four or eight neck-cells, 
which open flush with the surface, and have a canal-cell ” 
as before forced between them. 
Fig. 3. — Diagram of endogenous protballium of Selaginella, with few ar- 
chegonia, reduced each to an oosphere with four or eight neck-cells as 
a “ rosette ” above, and with canal cell between. Before the rupture of 
the apex to the expose prothallus, a large-celled, delicate “ endosperm ” 
(end) forms below the prothallus, apparently independent of it. 
These neck-cells form a kind of rosette,’’ as it has been 
termed, capping the oosphere which is sunk in the pro- 
thallus. But before the prothallus and its archegonia are 
exposed at the ruptured apex of the spore, a process occurs 
w^hich results in the formation of an apparently new 
structure. 
In Salvinia, Marsilea, &c., the space between the pro- 
thallus and the endospore, filling up the major part of the 
macrospore, becomes occupied by imbibed fluid, which accu- 
mulates and serves to push the prothallus upwards to the 
exterior, as it presses upon the diaphragm ” or membrane 
separating them. In Selaginella, however, a formation of 
large, thin-walled cells occurs in the fluid filling this space, 
and thus the so-called endosperm ” (Fig 3, end.) is pro- 
duced. At a later period its cells become crowded with 
food material for the nourishment of the embryo, as this is 
pushed down by its growth and that of its suspensor.” 
Our next step is to the Gymnosperms — the Conifers and 
their allies. Neglecting minor variations in detail, a typical 
Conifer presents the following features : 
Its microspores^ or pollen grains are produced not only in 
special and separate sporangia or pollen- sacs, but also on en- 
' For further information as to these homologies, &c., the literature 
quoted may be consulted. 
