96 
PROFESSOR A. ANSTRUTHER LAWSON ON 
prothallus. Another feature to be observed in this figure is the presence of an 
endophytic fungus in the prothallial cells. Many cells, even from the surface view, 
show the presence of this fungus. 
The internal tissue of the prothallus shows very little differentiation. The 
cells appear to be all very much alike. The external or “ epidermal ” layer is slightly 
different from the other cells, by reason of more sharply defined and slightly thicker 
outer walls. Apart from this slight difference, one may see that the prothallial tissue 
is practically uniform throughout. Each cell contains a finely granular colourless 
cytoplasm and a small but deeply staining nucleus. There is clearly no differentia- 
tion of the body of the prothallus into vegetative and reproductive regions which is 
so characteristic of the prothallus of Lycopodium. The antheridia and archegonia 
were found upon all surfaces, and, like the rhizoids, apparently developed quite in- 
discriminately. They were not confined to any particular region or surface. In fig. 3 
is represented a fair sample of a transverse section of the prothallus. It will be seen 
that the prothallus is approximately cylindrical, with a definite layer of superficial 
cells. Many of these superficial cells develop into rhizoids. Nuclei and protoplasm 
are present in the majority of the cells. But, as shown in the section, many of 
the cells are infected with an endophytic fungus. The section here represented was 
taken from near the apex, and the tissue is therefore not very old. It will be noticed 
in this young tissue the endophytic fungus has not spread to any great extent, and 
the superficial cells seem not to be infected at all. In fig. 4, however, which was 
taken from an older region of the same prothallus, the infection of the fungus has 
spread to practically all of the internal cells. Only the superficial cells are free, and 
even these in older conditions become infected. 
A careful examination of the fungus with the higher power of the microscope 
shows it to be of a non-septate nature. The hyplise are therefore very probably of a 
phycomycetous fungus somewhat resembling Pythium. A more highly magnified 
representation of the effect of the fungus in the prothallial cells is shown in fig. 6. 
This figure was drawn from cells very near the centre of the prothallus. It will be 
seen that in many cases the nucleus disintegrates and eventually disappears. All 
stages in these changes may be observed from any section from an old prothallus. 
Eventually the cell cavities become almost filled with the fungal hyphse and the cell 
walls become a dark-brown colour. From these studies there is little doubt in 
my mind that, while there may be an advantage, in the matter of nutrition, to the 
prothallus as a result of the association with the fungus, the parasitic nature of the 
hyphse eventually results in the destruction of the cells infected. In the older 
regions of certain specimens the cells showed no signs of being alive, but their 
cavities were filled' with hyphse, which in their turn showed signs of disintegration. 
It seems quite probable that the prothallial cells become infected from the ex- 
ternal substratum by way of the rhizoids. In many specimens examined the hyphse 
of the fungus were observed extending through the entire length of rhizoids, and 
