114 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 fliiviatilis^ for 

 instance, they are sometimes almost tendril-like^, 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^. 

 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 (jh) 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. 116. 



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 suhulatus simulates such an Alga as Bostrychia 

 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. (19 10). 2 Matthiesen, F. (1908). 



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



