274 WILLIS : MORPHOLOGY OF THE PODOSTEMACEÆ 
also describes in this paper two species of Lawia. L. 
foliosa is correctly described ; it has a flat creeping thallus 
composed of combined shoot structures (as in some Castel- 
navias), and bearing flowers. We shall see below that this is 
also the case in L. zeylanica, but in the spirit material of this 
Ceylon species, which was all that Prof. Warming had for 
examination, and also in the specimens preserved in 
herbaria, the growing points were not present, and so the 
true nature of the thallus was misunderstood, and it was 
described as a “ root ” structure like that of Hydrobryum 
olivaceum. 
In his fifth paper, Warming deals with Tristicha hyp- 
noides, a form widely distributed over the world, and 
having a peculiarly complex form of shoot arising from 
a creeping root. He also describes several new species 
of Mourera, Podostemon, &c., and creates a new genus, 
Leiothylax. 
Finally, in his sixth paper. Prof. Warming describes 
several new species in detail, establishes several new genera 
upon the Indian material, as already described in my first 
paper, and deals with the morphology of Marathrnm. He 
also describes the Indian species Griffithella Willisiana 
(Hookeriana, var.) and Hydrobryum lichenoides (Polypleu- 
rum acuminatum,Wmg.). This paper ends with a discussion 
of the classification of the order, which has been already 
mentioned in my preceding paper so far as it concerns the 
Indian forms. 
But little has been written by any other authors on the 
general life-history or ecology of the Podostemaceæ. The 
most readable account is that given by Goebel (I3j, who 
describes the plants from his own observations in British 
Guiana. He also points oat again, what was first noticed by 
Weddell, that the range of distribution of the species is, as a 
rule, very limited, and that even in one river there may be a 
different set of species or forms at each successive cataract. 
He describes the way in which the Podostemaceæ grow only 
in rapids, flowering when the fall of the water level expose 
