59 
The Podostemaceae of India and Ceylon. 
climatic conditions the subject is not so clear. Some of the 
characteristic members of the Connacian group are, however, 
undoubtedly frigofuge and their distribution is corresponding. 
Further parallels between isophytic and isothermal lines may be 
drawn without difficulty amongst the southern and western plants. 
Nevertheless much information is still wanting before we can 
determine how far the present distribution of the flora has been 
effected by conditions of climate. 
THE PODOSTEMACEAE OF INDIA AND CEYLON. 
I T is no easy matter to elucidate the extremely complex 
morphology of an order like the Podostemaceae and botanical 
science is indebted to Mr. Willis, for a valuable contribution 
towards the knowledge of this interesting group of aquatic plants, 1 
which is so completely adapted to a life in rushing water. In fact 
the habitat of the Podostemaceae is so unique, that their only 
competitors are a few specialised Bryophytes: and since the different 
genera are adapted to water of different speed there is even little 
struggle for existence amongst the various members of the order. 
Such a state of affairs has allowed of an extreme of morphological 
differentiation only paralleled elsewhere in the vegetable kingdom 
amongst the seaweeds, whose external morphology is frequently 
copied to a considerable extent in the vegetative organs of the order 
in question. 
Except in the concluding remarks, Mr. Willis’s paper deals 
only with the Podostemaceae of India and Ceylon, and the 
forms there represented are amongst the most specialised of the 
order. This specialisation, which evinces itself in the more or less 
extreme dorsiventrality and flattening of the horizontal portion 
and reduction in size of the secondary shoots of the plants in 
question, is regarded more as an adaptation to the dangers of a 
life in flowing water, than to the rapid current itself. Plants, such 
as the Podostemaceae, which live in a rapidly-flowing stream, are 
continually exposed to the danger of a fall of the water-level and 
are also probably subjected to a considerable scour. Mr. Willis 
points out that many of the South American Podostemaceae, which 
have well-developed leafy shoots, live in very swift water, so that 
1 J. C. Willis. Studies in the Morphology and Ecology of the 
Podostemaceae of Ceylon and India. Annals of the Royal 
Botanic Gardens, Peradeniya. Vol. I., part 4. September 
1902. (Plates iv.—xxxviii.) 
