328 



MOSSES AND FERNS 



CHAP. 



plant exceeds the leaves. In a plant with the fourth leaf still 

 unfolded, there were six fully-developed roots. 



The gaps in the vascular cylinder become more and more 

 prominent as the sporophyte develops, and there is finally 

 formed the wide-meshed reticulate cylinder found in the adult 

 sporophyte. 



In some Ferns, e. g., Pteris aquilina, there are developed 

 medullary steles which arise from the inner surface of the 

 primitive stelar tube. (See Jeffrey (3), pp. 133, 134)- 



Fig. 181.— a, Vertical longitudinal section of the apex of a rhizome of Adiantum 

 emarginatum, X2S; B, the central part of the same, Xi8o; L, a young leaf; C, 

 cross-section of a similar stem apex, Xi8o; D, apex of a young leaf of Onoclea 

 struthiopteris, showing the apical cell (jr). 



The Mature Sporophyte 



The Stem 



The stem in most of the Polypodiacese is either an erect or 

 creeping rhizome which, unlike that of the Eusporangiatae, often 

 branches freely. These branches are almost always formed 

 monopodlally, and are usually of the same structure as the main 

 axis; but in O. struthiopteris great numbers of peculiar stolons 



