304 



FILICALES 



[CH. 



are in striking contrast to the broader pinnules of the sub- 

 merged foliage leaves. Leaf-form is in many cases obviously 

 the expression of environment; the xerophilous fern Jamesonia^ 

 from the treeless paramos of the Andes ^ is characterised by 

 its minute leaflets with strong revolute margins and a thick felt 

 of hairs on the lower surface; in others, xerophilous features take 



Fig. 23.5. Hemitelia capensis K. Brown. Nat. size, a. Pinna of normal frond. 

 [From a specimen in the British Museum. M.S.] 



the form of a covering of overlapping scales (Ceteracli), or a 



development of water-tissue as in the fleshy leaves of the 



Himalayan fern Drijmoglossum carnosum. In the Bracken fern 



Boodle^ has shown how the fronds may be classed as shade and 



1 Goebel (91) PI. xni. - Spruce (08) ii. p. 232. •' Boodle (04). 



