264 



PLANT MORPHOLOGY 



Fig. 219. Cross section of the stelar portion of the root of Ophioglossum calif or nicum, 

 showing the thick-walled xylem in contact with the thin-walled phloem, both surrounded by 

 the pericycle and endodermis, X250. 



Fig. 220. Cross section of the stelar portion of the root of Botrychium virginianum, show- 

 ing four xylem groups, X 150. 



sides of the blade or only on the lower side. In O'phioglossum the root is 

 very simple in structure, generally having but one xylem group and either 

 one or two phloem groups (Fig. 219). In Botrychium the root has two to 

 four xylem groups (Fig. 220), in Helminthostachys four to seven. The 

 roots of all genera are exarch and without secondary thickening. 



The vascular anatomy of the stem is of an advanced type. In Botrych- 



