26 
Choice Ferns for Amateurs. 
open at the top, and communicating' witli the cavity 
below by means of a central canal. The cavity or 
sac at the base further contains a globose utricle; it 
surrounds the oosphere, which is regarded as the 
object to be fecundated, or as the germ that, after 
impregnation, will set up a g'rowth which ultimately 
assumes the form of the parent plant. 
Careful observations have shown that the fecun- 
dation of the oosphere is effected as f ollow^s : The 
tube of the neck of the archegonium is at first filled 
with a narrow cell (the canal-cell), the cell-wall of 
Fig. 22. Longitudinal! section of mature'archegonium of Fern, 
showing c, opening of canal jdown necK ; e, e, epidermis of 
prothallus ; n, necK=cells ; o, oosphere (much magnified). 
which becomes mucilaginous, swells, and is ex- 
pelled from the outer opening of the tube, leaving a 
passage for the antherozoid down the tube, or 
central canal, to the oosphere, when the latter is ripe 
to be acted on by it (Fig. 22). The antherozoids 
are caught in the mucilage while moving over the 
prothallus; they wriggle down the tube, reach the 
oosphere, and fertilise it. The oosphere very soon 
begins to grow, and the final result is the develop- 
ment of the oospore into the leafy plant or Fern. 
It may be mentioned that the oospore, at a very 
early period, divides into eight cells, in two layers. 
Of these cells, four lie next the base, and four next 
the front, of the prothallus. Of the latter, the two 
c 
