1 75 
Azolla filiculoides , Lam . 
central conical mass of the epispore at the top of the spore, 
which here seems to become soft ; Fig. 50 shows a cross- 
section of this mass with the top of the archegonium showing 
through the ragged triangular opening in the epispore. In 
this way the opening of the archegonium is left free for the 
entrance of the spermatozoids. 
Cross-sections of the prothallium are more or less decidedly 
triangular, with one angle longer than the others (Fig. 54). 
This longer angle corresponds to the ‘ sterile third ’ of the 
prothallium of Salvinia , and represents the first cell cut off 
from the prothallium-mother-cell. 
In case the first archegonium is fertilized at once, no others 
seem to be formed ; but in the great majority of cases 
examined by me, the first archegonium was not fertilized, and 
a varying number of secondary ones had been formed. The 
first of these arises close to the primary one ; indeed, its 
central cell is generally separated from that of the primary 
one by but a single layer of cells. The third arises near the 
base of the larger lobe (Fig. 54 a 3). In case all of these 
remain unfertilized, others arise between them, apparently 
without any regularity, as any superficial cell apparently can 
give rise to an archegonium. Nothing resembling the regular 
meristem of Salvinia could be detected, and after the first 
three, the other archegonia seemed to arise indifferently at any 
point in the upper surface of the prothallium. 
The Archegonium. 
The archegonium-mother-cell becomes early distinguished 
by its larger size, denser contents, and larger nucleus, from its 
neighbouring cells. It varies a good deal in size and shape, 
and the later-formed ones are decidedly smaller than the first 
and second. Sometimes the mother-cell is short and square 
at the bottom, and sometimes deep and narrow with a pointed 
lower end. Its development corresponds closely to that of the 
other Filicineae, especially Salvinia to which it bears a very 
strong resemblance. As in the primary archegonium, no basal 
