n 4 PODOSTEMACEAE [CH. 



selves against the substratum, form firm attachment organs. 

 They also secrete a kind of cement which renders their 

 adhesion to the rock very close and permanent. These haptera 

 are found in many Podostemaceae. In Mourera fluviatilis, for 

 instance, they are sometimes almost tendril-like 1 , while in 

 certain cases they serve as storage organs for reserve carbo- 

 hydrates 2 . 



In many of the Podostemaceae the creeping root discards its 

 root characteristics even more completely than in the Tristi- 

 chaceae, and becomes converted into a thallus, which either 

 follows out every irregularity in the substratum, or, remaining 

 more or less free, develops into all sorts of curious shapes 3 . 

 It still produces secondary shoots bearing leaves, but as the 

 root thallus becomes more important, the secondary shoots 

 become less so, until, in such genera as Hydrobryum (Fig. 76), 

 Farmeria, Dicraea (Fig. 77 and Fig. 79, p. 1 16), and Griffithiella 

 they are much reduced, and assimilation is mainly performed 

 by the thallus. A seedling of Dicraea stylosa, with the young 

 thallus (/^.) developed as a lateral outgrowth from the hypocotyl 

 (hyp.\ and bearing secondary shoots (s.s.~) is shown in Fig. 78 ; 

 the mature plant is represented in Fig. 79, p. 1 16. 



The thallus of the Podostemads is sometimes amazingly 

 polymorphic; its capacity for developing in exceptional forms 

 depends, apparently, on the fact that it is not restricted by a 

 rigid skeletal system, and that nearly all the cells possess the 

 capacity for renewed meristematic activity. Griffithiella Hooker- 

 iana, for instance, has a thallus which may develop into various 

 shapes recalling different Algae that grow in moving water; 

 one of its forms resembles the basal cup of Himanthalia lorea. 

 Farmeria metzgerioides, again, recalls Delesseria Leprieurii, 

 while Podostemon subulatus simulates such an Alga as Eostrychia 

 Moritziana, which also grows in rapids. Willis, who draws 

 attention to these cases of simulation, alludes to the great 

 difficulty of interpreting such resemblances between plants far 



1 Went, F. A. F. C. (1910). 2 Matthiesen, F. (1908). 



3 See Willis, J. C. (1902) for further details. 



