On a Prothallus provisionally referred to Psilotum 
BY 
WILLIAM H. LANG, M.B., D.Sc., 
Lecturer in Botany at Queen Margaret College , University of Glasgow . 
With Plate XXXVII. 
HE only important group of the Pteridophyta in which the sexual 
X generation is unknown is that of the Psilotaceae, comprising the 
two existing genera Psilotum and Tmesipteris . While travelling in 
localities in which Psilotum occurred, I spent considerable time in ex- 
amining the neighbourhood of the plants met with in the hope of finding 
specimens of the prothallus. The sporophyte was found growing in various 
situations in a number of localities. In Ceylon it was once or twice seen 
growing in the soil below coco-nut trees near the coast, and very abun- 
dantly on the masses of roots which form the swollen base to the stems 
of these palms. In the mountain region it was seen growing as an epiphyte, 
its rhizome spreading through the humus accumulated in the fork of a tree, 
and occasionally growing on rocks. The observations made in Ceylon 
were without result ; in most cases the start of any isolated portion of 
rhizome could be best accounted for by an origin from one of the gemmae 
borne in large numbers on the rhizome. In the localities I visited in the 
Malay Peninsula 1 Psilotum was not abundant, but in one of them, Maxwell’s 
Hill in Perak, a number of plants were found growing on the stems of tree- 
ferns. The rhizome was embedded among the adventitious roots covering 
the stem of the tree-fern, while the aerial shoots projected more or less 
from the surface ; they were not flattened, so that the species was presumably 
P. triquetrum. In close association with one of these plants the single 
prothallus, on the study of which the following description is based, was 
found. A preliminary account of its external form has already been 
published 2 . 
1 The scientific expenses of my expedition to the Malayan Peninsula were met by a grant of the 
Royal Society. 
2 Proc. Roy. Soc., vol. lxviii, 1901, p. 405. 
[Annals of Botany, Vol. XVIII. No. LXXII. October, igo4-] 
