PTERIDOPHYTA 



263 



thostachys is palmately divided. Except in Botrychium virginianum, the 

 leaves are fleshy. The blade has many veins that in Ophioglossum are 

 reticulate but in the two other genera branch dichotomously and end 

 freely. At the apex of the rhizome is a large bud containing the primordia 

 of leaves that expand diu'ing the next four or five seasons. In all genera 





Fig. 218. Botrychium dissectum, about one-half natural size. (From Chamberlain.) 



the stem tip and each successive leaf are ensheathed by the base of the next 

 older leaf. The vernation of the Ophioglossales is not circinate, as in the 

 higher ferns, but erect. Both the root and stem increase in length by 

 means of a tetrahedral apical cell. 



Vascular Anatomy. The leaf blade is simple in structure, with an 

 epidermis enclosing uniform mesophyll. Stomata may occur on both 



