576 Lang. — On a Prothallus provisionally referred to P silo turn. 
approaches most closely to the wholly saprophytic subterranean type, and 
in the differentiation of its fungus-containing region is practically identical 
with Lycopodium complanatum\ It does not resemble closely any of the 
prothalli of tropical species hitherto described. Its form and structure 
would, however, be quite consistent with its belonging to some tropical 
species of Lycopodium , the life-history of which is at present unknown. 
The only other possible position to assign to this prothallus is to regard 
it as belonging to Psilotum. Since direct evidence is lacking, we can only 
estimate the probability of this view indirectly. I shall therefore simply 
state in conclusion the reasons which incline me to provisionally assign this 
prothallus to Psilotum rather than to some species of Lycopodium. I 
recognize fully that no decisive weight can be attached to the arguments 
which follow, and that it must be left to future research to confirm or 
disprove my view. 
In the first place, it appears to me that considerable weight may fairly 
be attached to the close association of the prothallus with a plant of 
Psilotum. It was found a few inches from this plant, embedded, as the 
rhizomes of the latter were, among the roots of the tree-fern. In my short 
stay in the locality I did not observe any species of Lycopodium growing in 
the same situation, though of course such may occur. My personal 
experience of searching for prothalli of Lycopodium would not lead me to 
expect those of any species to be so common as to be likely to turn up in 
situations not as a rule occupied by the sporophyte. At least I should regard 
the chances as being against a single prothallus found close to a plant of 
Psilotum being one of a species of Lycopodium sown from a distance. 
I incline to regard it as more probably related to the plant of Psilotum in 
its immediate neighbourhood, though I should hesitate to express an 
opinion as to whether it had sprung from a spore of this plant or whether 
the latter had originated from another prothallus sown at the same date. 
Our knowledge of the rate of growth alike of Psilotum and of saprophytic 
prothalli of this type is too imperfect to help us to come to a decision. 
In the second place, the prothallus under consideration may, so far as 
generalizations are possible on the subject, be regarded as belonging to the 
wholly saprophytic subterranean type, such as that of Lycopodium clavatum 
or L. complanatum. It is remarkable to find such a prothallus in a situation 
to which a prothallus of the type of L. Phlegmaria would appear better 
adapted. But when the range of situation in which the plants of Psilotum 
are known to occur is taken into consideration this difficulty would admit 
of a satisfactory explanation. Psilotum is not an obligative epiphyte ; it is 
known to grow in soil, and it would not be surprising if its gametophyte 
were of the subterranean type. 
On these grounds I am disposed to regard it as probable that this 
1 Bruchmann, loc. cit., Taf. 5. 
