504 



A TEXTBOOK OF THEORETICAL BOTANY 



at the point of dichotomy of the stem, a feature which is not uncommon 

 in the FiUcales. It is secondarily shifted on to the weaker hmb of the 

 dichotomy, on which it appears to arise, but its vascular system is connected 



Fig. 4g^.—Pteridium aqiiilimtm growing in a wood. Much reduced. 



(From Step, " Trees and Flowers of the Countryside," Hutchinson &^ Co. Ltd.) 



directly to that of the main stem. This is the reverse of the condition found 

 in Dryopteris, where the lateral buds are attached to the leaf petioles. 



The rhizome has definite upper and lower sides, that is, it is dorsiventral. 

 It bears leaves alternately to right and left as well as adventitious roots. 



The leaves are very slow to mature. During the first year only an inch 

 or so of the petiole develops and there is no lamina (Fig. 498). During the 



