290 WILLIS : MOKPHOLOGY OF THE PODOSTBMACEÆ 
As may easily be conceived, and as Warming has pointed 
out, the anatomy of these plants, with their highly organized 
dorsiventral thalli and their peculiar habitat and mode of 
growth, is of great interest. To deal with it in detail in this 
paper would, however, enormously increase its already con- 
siderable bulk, and therefore I have dwelt only lightly on 
the anatomical features, so far as they are necessary for the 
treatment of the general morphology, reserving details for a 
later paper. The same statement applies to developmental 
features of the flowers, &c. 
The genera will now be dealt with in the following order ; 
Tristicha, Lawia, Podostemon, Dicræa, Griffithella, Willisia, 
Hydrobryum, Farmeria. 
TRISTIGHA. 
[Du Pet. Th. ; Willis, Rev. Podost, Ind., Ann. Perad. I., p. 207.] 
This almost cosmopolitan tropical genus is represented in 
India by the single species T. ramosissima (Wight), Willis, 
found in Travancore and Malabar, and to which I have given 
a separate sub-genus Dalzellia. The other two species of 
Tristicha are placed in a sub-genus Eutristicha» 
Cario (8) has described the anatomy and to some extent 
the morphology of the widespread form T. hypnoides. This 
he collected among mosses in a stream in Guatemala, grow- 
ing in little tufts. He commences by criticising the 
accuracy of Tulasne’s figure (39), but, as Warming points out, 
both authors are right in general ; we have here one of the 
many cases of confusion that have been caused by the 
complex morphology and the polymorphism of these plants. 
Cario describes the creeping root- or rhizome-like structure 
which is closely attached to the rock, and which bears the 
tufted leafy shoots, on which latter the flowers arise. He 
names this creeping organ the thallus, and regards it as an 
organ sui generis — not a root, because it has no cap, and not 
a shoot, because it has no leaves. He describes its branching 
as endogenous. It is traversed by a single vascular strand, 
