The Anatomy of Psilotum triquetrum. 
BY 
SIBILLE O. FORD, 
Newnham College , Cambridge ; and Robert Platt , Research Scholar , 
Owens College , Manchester . 
With Plate XXXIX. 
T HE genus Psilotum is represented by four species, P. triquetrum , 
P. jlaccidum , P. complanatum , and P. capillare. Baker T , however, 
gives only two distinct species, P. triquetrum and P. complanatum , regard- 
ing P. capillare as merely a variety of P. triquetrum , and, similarly, P .Jlac- 
cidum of P. complanatum. Of these, P. triquetrum appears to be the most 
frequent in occurrence, being reported from practically all the warmer 
regions of the world 1 2 . The plant is found growing in the humus at the 
base of trees, amongst the roots of tree-ferns, and in the crevices of rocks. 
It is generally regarded as an epiphyte ; but as young plants which had 
developed from bulbils, and also portions of the underground rhizome which 
had been broken off from the main plant, have been known to vegetate 
underground for a considerable length of time 3 , the plant may also 
be regarded as being saprophytic in nature. A small, but well-developed, 
specimen grew for some time in the soil amongst the roots of Norantea 
guianensis in one of the tropical houses at the Cambridge Botanic Garden. 
It was unknown how the plant originally came there 4 S . 
External Morphology. 
The plant consists of a much-branched, green, aerial stem bearing the 
sporangia and small reduced leaves, and a brown underground rhizome, 
which is likewise much branched. There are no roots. 
1 Baker (’87), p. 30. Willis (’97), p. 314. 
2 Spring (’49), p. 269, et seq. Bertrand (’81), p. 257. 3 Solms-Laubach (’84), p. 141, 
4 Mr. Lynch tells me it is probably due to small pieces of the rhizome being broken off during 
potting, and one of these may have been unintentionally mixed with the soil in the pot of the 
Norantea. 
[Annals of Botany, Vol. XV III. No. LXXII. October, 1904.] 
S S 2 
