CH. ix] HABITAT OF THE PODOSTEMADS 113 



distinct family, occurred when Aublet 1 , nearly a century and a 

 half ago, discovered Mourera in rapidly running water in French 

 Guiana. In the case of a certain Venezuelan river, Goebel 2 

 describes the bed, in places where the water flows quickly, 

 as quite green with a Podostemad, Marathrum utile^ growing on 

 the stones, and he points out that it flourishes more freely the 

 stronger the current; when the stream is slow it is replaced by 

 Mosses and Algae. Another writer 3 observed Mourera fluvia- 

 tilis in the cataracts of a tributary of the Amazon, growing in 

 such abundance that the rocks, amongst which the waters 

 rushed, were veiled by it, and the colour was so vivid that the 

 river seemed to use his own expression "to flow over a carpet 

 of roses." This red hue of the vegetative organs, due to antho- 

 cyanin in the surface cells 4 , has been noted in many cases. 

 Miss Lister 5 , for instance, in her account of the occurrence of 

 a species of Tristicha in rapidly flowing water below the first 

 cataract of the Nile one of the rare records of the appearance 

 of a member of these families outside the tropics mentions 

 that, when the plant was wet and fresh, the colour was crimson. 

 The majority of the peculiarities of the Podostemaceae and 

 Tristichaceae are closely related to the nature of their habitat. 

 Life in rushing water on rocks which are often water-worn 

 to smoothness and into which no roots can penetrate is 

 obviously impossible except to plants which have a special 

 capacity for clinging to the substratum. In the Tristichaceae 4 

 (e.g. Tristicha ramosissima and Weddellina squamulosd) a creeping, 

 thread-like organ is formed, which, though morphologically a 

 root, is dorsiventral in structure, and gives rise to leafy shoots 

 endogenously in acropetal succession. But this thread-like root 

 is not apparently competent to anchor the leafy shoots with the 

 necessary firmness, and additional organs called ' haptera * are 

 formed. They are produced exogenously from the creeping root, 

 and by their positive geotropism and power of flattening them- 



1 Aublet, F. (1775). 2 Goebel, K. (1891-1893). 



3 Weddell, H. A. (1872). 4 Willis, J. C. (1902). 



5 Lister, G. (1903). 



A. w. P. 



