OF CEYLON AND INDIA. 
303 
ribs in corresponding places, and after fertilization a fruit of 
exactly similar type is produced {cf. below). 
Rejuvenescence . — To what extent rejuvenescence, Le., the 
formation of new growing points if the old ones are damaged, 
and the consequent resumption of growth of the thallus and 
formation of new secondary shoots, takes place in this 
species, I do not know, but there is evidence upon the 
material in my hands to show that it does take place, and 
probably it is common enough, as in the Ceylon forms. 
Before going on to the next genus, we must briefly cou“ 
sider the morphology of Tristicha in connection with its 
ecology, or in relation to the general conditions of life. All 
three species seem to be very similar both in morphology 
and ecology. Comparing these plants with most other water 
plants, it is evident that they are as highly modified to suit 
a submerged existence as any others, and that they may 
well be compared with the members of such families as the 
Ceratophyllaceæ. They show most of the characters one is 
accustomed to look for in submerged plants, e.g., much 
vegetative growth, frequent branching, great vegetative 
reproduction, absence of stomata, reduction of vascular 
tissue, especially of the water-carrying elements, central 
vascular bundles, delicate leaves, chlorophyll in the epi- 
dermis, absence of palisade tissue, &c. On the other hand, 
they show a few marked features which are not usually 
present in such plants. 
To take these in order, the thallus, speaking in the ordi= 
nary sense, is evidently morphologically a creeping root, 
such as in other water plants and even land plants is not 
uncommon, where the primary root owing to the mode of 
growth in relation to the substratum is unable to develop 
in the ordinary way, and is replaced by adventitious roots 
laterally developed. This development is carried to an 
extreme in the plants now under consideration, as the root 
is used as the means of large vegetative multiplication of 
