ii8 



PODOSTEMACEAE 



[CH. 



J>c- 



for this view. That these plants, with their large stores of 



reserve starch, are, as a matter of fact, liable to be preyed upon, 



is indicated by Im Thurn's^ observation that, in British Guiana, 



when the rivers are low, and the rocks which underlie the rapids 



are partially uncovered, a certain fish (Pacu myletes) collects at 



the falls to feed on the leaves of 



the Podostemads, which clothe the 



rocks, and at this time of year 



come into flower. This fact is so 



well known that, at this season, 



large numbers of Indians camp on 



the sides of the falls, in order to 



seize the opportunity of shooting 



the fish. 



The most important anatomical 

 peculiarity of the Podostemads is 

 the extreme reduction of the inter- 

 cellular spaces^; in this respect 

 the members of these families 

 contrast most markedly with other 

 water plants (Fig. 80). This feature 

 is probably to be associated with 

 the thorough aeration of the tor- 

 rential water which they frequent^. 

 Certain species, however, possess 

 delicate outgrowths from the sur- 

 face of the leaves which have been 

 interpreted as "gill-tufts" (Fig. 

 81). Possibly these structures to 

 some extent compensate for the lack of an internal aerating 

 system. 



The water in which the Podostemaceae live is liable to 

 variations in level, and their habit of blooming when the sinking 



y&.- 



Fig. 80. Dicraea stylosa, Wight, f. 

 fucoides, Willis. T.S. thallus to show 

 absence of intercellular spaces. ep.= 

 epidermis ; p.c. parenchymatous 

 cortex;?;. &.= vascular bundle, (x 150 

 circa.) [Wilhs, J. C. (1902).] 



1 ImThurn, E. F. (1883). 

 ^ See pp. 256, 257. 



Warming, E. (1881). 



