288 WILLIS: MORPHOLOGY OP THE PODOSTEMACEÆ 
fern or an Eriocaulon. In the dry season, when the water- 
level fall slow enough to bring the Podostemaceæ to the surface, 
they become covered with filamentous algæ, but by this time 
it can matter but little to their success or life. These plants 
escape from competition to a degree that is very rare in the 
vegetable kingdom. They hardly even compete with one 
another for position, as each species on the whole affects, as 
already mentioned, its own »particular kind of locality, and 
only to a small extent mixes with others. This absence of 
competition is probably a very important factor in the 
morphological features of these plants ; they have been 
enabled to adapt themselves structurally, mainly in relation 
to the physical factors of their environment, rather than to 
the biological. 
Animal life also seems to have but little effect on the 
Podostemaceæ. The movement of the water is too swift to 
alloAv them to be attacked by fish, and the only animals that 
seem to have any effect are the larvæ of various water insects; 
these feed greedily on the thalli, which are usually very rich 
in starch. Indirectly, wading birds are probably of much 
importance, because they walk about on the rocks with wet 
feet in the dry weather, and the small sticky seeds must cling 
to their feet, and thus probably be at times carried to suitable 
places for growth in other localities. 
Evidently, then, we have in the Podostemaceæ a group of 
plants of singular morphological and ecological interest, and 
one in which there is still a very large field of work open to 
modern methods of research in these lines. The present 
paper hardly does more than clear up the darkness that has 
hitherto surrounded these organisms in regard to many inter- 
esting features of their life-history and general morphology, 
leaving a vast amount of work still to be done. 
Not merely are these plants directly interesting in them- 
selves, but they afford a group in which the connection 
between the change in morphology and the changed ecology 
can be well studied, as we have already a very fair knowledge 
