CHAPTER XX 



Ferns 



lugh exhibiting a marked advance in organ- 



TiiE Bryophyta, thd with the Thallophyta, differ from the 



isation as compare plants, comprised in the third class of the 



remaining flowerlef;^ or Pteridophyta, in lacking roots and true 



Vegetable Kingd'-In the Pteridophyta, moreover, the gameto- 



vascular tissue.- thalloid in form and short-lived, whilst the 



phyte is usual phase in the life-history is far more conspicuous 



spore-produciranent, and is quite independent of the gametophyte 



and more per very earliest stages. In the sexual process and 



except in i structure of the sexual organs, however, there is 



the generic correspondence between the two classes, the Pteri- 



consideralike the Bryophyta, possessing motile male cells, and 



dophytaending on the presence of hquid water at the time of 



thus deion. The Pteridophyta, as a matter of fact, in general 



fertilismoist habitats, although rpite a considerable number 



favourw under relatively dry conditions. Included in this class 



can g'e Ferns (Filicales), the Horsetails (Equisetalcs) , and the 



are tosses (Lycopodiales), of which the first-named will be 



Club/.ered in the present chapter. 



consi many common Ferns the stem is an underground rhizome, 

 1 is relatively insignificant in comparison with the con- 

 whious, usually deeply divided, pinnate fronds which alone 

 spicir above the surface ; a notable exception is, however, 

 appted by the Tree Ferns of subtropical regions, which have 

 affonarked trunks. The subterranean stem is either horizontal 

 walk the Bracken, Pteris aquilina, Fig. 158, B), or compact 

 (as nore or less erect [e.g. Lady Fern, Athyrium filix-famina ; 

 andl Fern, Osmunda regalis). It rarely shows branching, 

 Ro3;h this occurs at intervals where the rhizome is elongated 

 tho-ig 2S9 



