THE GAMETOPHYTE GENERATION OF THE PSILOTACE^. 
99 
surface. In several instances the young archegonium was observed ; and in such 
cases the neck cells, consisting of four rows of four tiers each, formed a short tube 
with a rounded apex, as shown in fig. 2. A sectional view more highly magnified 
is shown in fig. 13. The position of the venter below the surface is indicated, and 
also the curious form of the lower tier of neck cells. It will be noticed that they 
spread slightly out and terminate in pointed margins. 
The surface view of the archegonia more highly magnified is shown in fig. 14. 
The four cells represented in each case are the lowest tier of neck cells mentioned 
above. The neck canal is a narrow channel surrounded by these four cells. The 
narrowness of the channel is due to the construction shown in fig. 13. The matur- 
ing of the archegonium and its preparation for fertilisation are very curious. In 
other Pteridophytes such as Equisetum, Lycopodium, or Botrychium the archegonium 
matures by the separation of the apical tier of cells and then spreading out to form 
a gaping channel down the neck of the archegonium. In Tmesipteris I was unable to 
find any evidence of this. In fig. 15, for instance, we have a representation of a 
mature archegonium ready for fertilisation. It will be observed that the main 
portion of the neck, consisting of the three upper tiers of cells, has been, torn away, 
leaving behind only the lower tier with the egg cell in the venter.' In fig. 16 we 
have represented a somewhat similar condition. The upper tiers of neck cells have 
broken away, but traces of the cell walls of the second tier are to be seen. A 
similar condition is shown in fig. 17. These three figures are fair samples of the 
appearance of the mature archegonia. There were scores of others observed. I 
was first inclined to think that these archegonia were injured in the handling of 
them, and that in removing the particles of soil from the surface of the prothallus 
the necks were broken off with the camel’s-hair brush. Having examined scores of 
prothalli — and many of these were handled with the greatest care — I am inclined to 
the belief that this breaking away of the upper part of the archegonium is a natural 
one, and not due to artificial causes. As shown in fig. 13, the lower tier of cells is 
sharply defined. As I have already pointed out, these cells extend slightly beyond 
the surface, and in section their margins seem to spread, giving the appearance of a 
constriction at this region of the archegonium. These four cells that are left form a 
fiat disc, slightly concave in the middle, but otherwise parallel with the surface of 
the prothallus. This of course results in a great shortening of the neck of the 
archegonium at the time of fertilisation, and it seems not unreasonable to interpret 
it as a special adaptation to meet the unusual conditions of subterranean fertilisation. 
PsiLOTUM. 
The Vegetative Features of the Prothallus. 
The method adopted for securing specimens of the prothallus of Psilotum was 
practically the same as that used in the case of Tmesipteris , with slight modifications 
