Fertilization in Collema . 
755 
in the thickness of the walls and their affinity for the orange is very similar 
to that described by Harper ( 18 ) for the antheridium of Phyllactinia, where, 
after the conjugation pore is closed, the wall of the antheridium increases in 
thickness by what seems to be mucilaginous degeneration. The swelling, 
too, is towards the interior of the cell. There is, however, a difference in that 
it is only the cross-walls of the trichogyne which gelatinize ; the side walls 
remain as before. In Phyllactinia the thickening is less in the region of 
the closed conjugation pore and greatest on the wall of the antheridium 
opposite this pore. The blue-staining terminal cells and the brown cross- 
walks of the trichogynes are very conspicuous even after the apothecium 
has been formed. The cells of the trichogyne maintain their cylindrical 
shape for some time, but by the time the thickening of the cross-walls is 
greatest the protoplasm of the cells has become denser, the plasma mem- 
brane is pulled away from the side walls, and these walls begin to bend in 
towards the centre of the cell, giving the cell somewhat the shape of an 
hour-glass. The cells are even more conspicuous now because their appa- 
rently disintegrating protoplasmic masses stain deep red. The cross-walls 
are gelatinized but remain as wide as ever. 
This change in the shape of the trichogyne cells was observed by Stahl, 
who thought it was connected with a loss of water and hence of turgidity. 
The disintegrating masses of protoplasm have the same appearance as that 
described for the antheridial cell of the Mildews and of the conjugation tube 
of Pyronema . Harper found that the cell sap disappears, allowing the 
denser portions to form a homogeneous mass which has then an affinity 
for the safranin. Harper also observed that as disintegration continued the 
mass stained less deeply, but that the brown walls were still conspicuous. 
This is true for my material. The brown cross-walls are still evident when 
the part of the cell between is scarcely noticeable. 
As to the sexual nature of the structures described, my investigations 
confirm those of Stahl, Baur, and Darbishire, and leave no doubt as to the 
functions of the trichogyne and spermatia. The behaviour of the trichogyne 
in this Collema should put an end to the idea of the trichogyne being either 
a respiratory apparatus or a boring organ. It is very evident here that the 
trichogyne is exactly what it is in the red Algae, a structure developed from 
the egg-cell to conduct the male nucleus to the egg-cell. The very apparent 
attraction of the trichogynes to the spermatia, and the later changes in the 
ascogone and trichogyne, show plainly also that the reproductive organs are 
functional. 
We may summarize the differences in the sexual apparatus of this 
form of Collema pnlposnm and that of all other Lichens so far described 
as follows : (i) The spermatia are reduced in numbers and are not enclosed 
in spermogonia. (2) The spermatia are embedded deep within the thallus 
and are never set free on its surface. (3) The trichogyne has fewer cells 
3 D 2 
