200 WILLIS : PODOSTEMACBÆ 
India. Later research may exclude these, but for the 
present they may best be regarded as species of Podostemon. 
They have simple leaves, but some of the American species 
have the same, and they show many points which, as 
compared with most of the Indian forms, seem primitive ; 
perhaps their position in the extreme south-west also 
indicates their antiquity. 
Under Podostemon, Warming and other authors include 
the curious flat lichen-like thalloid species, olivaceus, John- 
sonii, lichenoides, and the new species sessile. I have 
shown below that these forms are perhaps better placed 
under Hydrobryum, along with the solitary species H. 
Griffithii, left in it by Weddell, Hooker, Warming, &c., as the 
stigmatic character of this species is not constant and cannot 
be used as generic ; this genus will thus include species 
with smooth and ribbed fruits, and with iso- and hetero- 
lobous fruits. In most cases these difiterences are almost 
generic, but in this case they seem of less importance. A 
new genus, coming near to the thus extended Hydrobryum, 
is Farmeria, Willis, with one species in Ceylon (with a 
sessile, indéhiscent smooth fruit) and one in South India 
(with a stalked, ten-ribbed, dehiscent, anisolobous fruit). 
This is well marked, so far as we yet know, by its thallus 
morphology and few seeds. 
Now, take the genus Dicræa, merged in Podostemon by 
Bentham and Hooker ; is it to stand, and if so, what is it to 
include As defined by Tulasne, it has a ribbed isolobous 
fruit with both valves persistent, with one-flowered secondary 
shoots on a more or less dimorphic ribbon-like root 
thallus. Apart from the fruit, the flower resembles that of 
Podostemon. Under this definition comes a large group 
of nearly allied Indian species, fairly sharply marked off 
from any others : D. elongata, Wallichii, minor, dichotoma, 
stylosa. All these are very variable plants, but agree 
closely in many characters, possessing an exogenously 
branched ribbon-like thallus, partly floating freely in the 
water, with small one-flowered secondary shoots, leafy at 
