102 
PROFESSOR A. ANSTRUTHER LAWSON ON 
described for the sporophyte,* and it seems highly probable that each growing 
branch has a single apical cell. 
It is a matter of interest to note that none of the meristem cells or other cells at 
the growing point show any trace of the endophytic fungus (fig. 21). The region 
that is free from this fungus is, however, not great. Fig. 20, for instance, represents 
a transverse section taken not far from the apex, and here we see many of the cells 
filled with fungal hyphse. As in Tmesipteris, the infection spreads uniformly through- 
out the prothallus. There is no zone or region differentiated as an infected area. 
Fig. 20 represents a fairly typical section through any region of the prothallus except 
that at the growing point. Here we see the majority of cells harbouring the fungus. 
Fig. 22 represents a longitudinal section to show the distribution of the fungus from 
this view. In both transverse and longitudinal sections it was clear that the super- 
ficial cells are not frequently infected. A more highly magnified view of a few 
infected cells from the interior of the prothallus is shown in fig. 25. This illustrates 
the effect of the endophytic fungus on the cytoplasm and nuclei of the host cells. 
The fungus is clearly a parasite living on the protoplasm of the prothallus. It will 
be seen from this figure that in the more advanced stages the nuclei have completely 
disintegrated. Eventually the hyphse become coiled in dense masses, and fill the 
main space of the cell-cavities. When one compares this figure with fig. 6, which 
represents a corresponding condition in Tmesipteris , one is inclined to believe that 
it is the same species of fungus, or at any rate the same genus. Here it will be seen 
that the hyphse are non-septate, just as it is shown in figs. 5 and 6 described above. 
Here also the infection seems to be by way of the rhizoids. Numerous examples 
were found showing the long hyphal threads extending the length of the rhizoids. 
From the description of the vegetative characters of the prothalli of Psilotum f 
and Tmesipteris , it would be difficult to find two types more closely resembling one 
another. They have the same general form : they are subterranean, and devoid of 
chlorophyll ; they are both saprophytic and infected with an endophytic mycorrhizal 
fungus of the same type ; the distribution of the fungus in the tissues is the same in 
each-case. They have all these vegetative features in common, yet they do not bear 
a very close resemblance to other subterranean pteridophytic prothalli. 
The Antheridia. 
Abundance of material has been found for the study of the antheridia. Every 
prothallus procured bore these sexual organs. On some specimens these organs were 
* Solms-Laubach, 1884 ; Ford, S. O., 1904. 
| In his general account of the prothallus of Psilotum (see preceding paper, pp. 87-89), I quite agree with 
Mr Darnkll-Smith. 
Reference should also be made to a note published in the Proceedings of the Linnean Society of New South Wales. 
This is a note by Mr T. Whitelegge giving an account of an object which he believed to be the gametophyte of 
Psilotum triquetrum. This description has been referred to and fully quoted by Mr Darnell-Smith (p. 86). I will 
only add that I can fully endorse Mr Darnell-Smith’s observations, but have found nothing that in any way agrees 
with Mr Whitelkgge’s account. 
