SECT. I 



MORPHOLOGY 51 



The rhizophores of SelagineUa (Fig. 53) which have been variously- 

 interpreted as leafless shoots, as roots, and as organs sui generis, find 

 their place here. They resemble leafless shoots, attain a considerable 

 length, and may branch dichotomously and give rise to endogenous 

 roots close to the growing points. As a matter of fact they are in 

 structure and general behaviour intermediate between shoot and root, 

 and it is not probal)le that they have originated from either of these 

 primary members. 



Various outgrowths of the body of the plant to which an inde- 

 pendent origin is to be ascriljed are grouped together as emergences. 

 A phylogenetic significance cannot be attached to the term as here 

 used. It includes structures of the most different origin belonging 

 both to the thallus and the cormus. The rhizoids, which serve to 

 fasten the thallus of many Thallophytes and the moss plants to the 

 substratum, as Avell as the massive attaching organs of many Brown 

 Sea-weeds (Fucaceae and Laminariaceae) are classed here. So also 

 are the organs which arise as microscopically small structures on the 

 bodies of both lower and higher plants, and contain the asexual and 

 sexual reproductive cells of the Cryptogams (sporangia and sexual 

 organs). In the sense of the term implied here the hairs, prickles, 

 and glands borne on the surface of the highly-organised plants must 

 be included as well as the haustoria described above. As an extreme 

 case the attaching organs (hapter?e) of the previously mentioned 

 Podostemaceae may be referred to. These hapter?e serve to attach 

 the nutritive roots of these plants firmly to the rocks upon which 

 they grow exposed to rapidly flowing water. They are at first 

 conical outgrowths, but flatten out and become lobed when applied to 

 the surface of the rock. The shoots originate from the flat nutritive 

 roots. There is, indeed, no reason why various outgrowths of the 

 vegetative body of the plant should not become adapted to the 

 performance of particular functions. 



