OF CEYLON AND INDIA. 
•289 
of the morphology of the ordinary submerged plants of quiet 
waters. The most striking feature about their general mor- 
phology is the remarkable similarity which they exhibit to 
the lower forms of the vegetable kingdom, in particular the 
mosses, liverworts, and algæ, and in the latter more especially 
the algæ of moving water, such as the Fuci of the rocks on 
the sea coast. This similarity may be only “accidental,” or 
it may be due to the action of similar causes. The Podos- 
temaceæ are evidently very plastic, and we shall see in the 
Indian forms a series of plants of gradually increasing 
plasticity, and find that on the whole as the plasticity 
increases the plant becomes more and more like the lower 
vegetable forms. Once the plasticity is well established, so 
to speak, there seems little limit to it, the more so as these 
plants have no competition with other living organisms to 
modify their adaptation to the physical factors of their 
environment. 
We shall proceed to deal with the Indo-Ceylonese species 
in order. As described in the preceding paper, they belong 
to two widely separated groups, the Tristicheæ (Tristicha 
and Lawia) and the Eupodosfcemeæ (the other six genera). 
So far as possible the systematic order there given will 
be followed, but for the sake of simplicity of treatment 
certain genera and species will be described out of their 
proper order. We shall deal first in a general way with 
the genus, and with preceding literature relating to it, 
and then with its species. The habitat of each will be first 
described, then the dry season appearance, which hitherto 
has been the only one observed by botanists, then the 
germination if known, the development of the thallus, its 
morphology, the appearance of the secondary shoots, the 
life-history during the vegetative season, the development of 
the floral shoots, the opening, structure, and fertilization of 
the flowers, and lastly, the fruit, seed, and phenomena of 
rejuvenescence, with any other special features of biological 
interest. The genus as a whole will then be considered in 
relation to the general conditions of life. 
