OF INDIA AND CEYLON. 
203 
cataract, perhaps specifically. My own work on the Asiatic 
forms leads me to believe that this is generally true, and 
that when we shall ultimately have acquired a detailed 
knowledge of their morphology and life-history, we shall 
find that each river or group of rivers, if not each branch or 
section of each large river, has its own peculiar forms of 
each genus or species represented in it. Even from the 
comparatively small amount of material in my hands, a 
great number of species might easily be made by admitting 
as specific the well-defined differences between them. A 
vast amount of comparative work on the spot is required to 
thoroughly sift the question, and I therefore refrain from 
complicating the already tangled mass of taxonomic litera- 
ture by making numerous new species. I have rather, 
probably, erred in the opposite direction by drawing my 
specific limits very widely indeed. Under each I have 
mentioned most of the well-marked forms observed by 
myself in the various localities visited. 
With regard to the genera, I have adopted a somewhat 
different course, and have perhaps drawn my generic limits 
too narrowly, my object having been to indicate the groups 
into which the species naturally divide themselves. Probably 
further study and investigation of the doubtless numer- 
ous undiscovered species of South-east Asia and tropical 
Africa will bridge over many of the gaps, and clearly show 
which genera are to be finally retained as natural. 
Podostemaceæ Indices. 
Flowers hermaphrodite, regular 3-merous with perianth, or 
zygomorphic 2-merous without perianth, hypogynous, small, 
inconspicuous, anemophilous. Perianth when present (3), 
imbricate, sepaloid, equalling or exceeding ovary, marcescent. 
Achlamydeous flowers included before opening in a closed 
spathe, which opens irregularly at the tip or by a slit on the 
upper side. Stamens hypogynous, in regular flowers 3 
