SPHENOPSIDA III 



The root grows from an apical cell with four cutting faces, 

 the outermost of which gives the root cap. It may be triarch, 

 tetrarch or diarch in its vascular structure and there is 

 usually just a single central metaxylem element. The stele is 

 surrounded by a pericycle, whose cells correspond exactly in 

 number and radial position with those of the endodermis, 

 since they are formed by a perichnal division in a ring of 

 common mother cells. This has led to the statement that the 

 root has a double endodermis, but this is incorrect, since the 

 cells of the inner ring are without Casparian strips, and must 

 be regarded as pericycle. 



The cone (Fig. i6L) invariably terminates an axis, whether 

 it be the main axis or a lateral one, and bears whorls of 

 sporangiophores, without any bracts or other leaf-Hke 

 appendages interposed, although there is a flange of tissue 

 at the base of the cone called the 'collar'. Each sporangio- 

 phore is a stalked peltate structure, bearing five to ten 

 sporangia which, although having their origin on the outer 

 surface, become carried round during growth into a reflexed 

 position on the underside of the peltate head (Fig. i6M). 

 Within the cone axis, the vascular system forms a very 

 irregular anastomosing system, without discernible nodes 

 and internodes, from which the sporangiophore traces 

 depart without any regular association with the gaps. The 

 sporangiophore trace branches within the peltate head and 

 each branch terminates near a sporangium. 



The sporangium has its origin in a single epidermal cell, 

 which divides perichnally into an inner and an outer cell. 

 The inner cell gives rise to sporogenous tissue. The outer cell 

 gives rise to further blocks of sporogenous tissue and also to 

 the wall of the sporangium. Adjacent cells may also add to the 

 sporogenous tissue. The sporangium may therefore be des- 

 cribed as eusporangiate in the widest sense and at maturity 

 the sporangium is several cells thick. The innermost wall 

 cells break down to form a tapetum, as also do some of the 

 spore mother cells, and the ripe sporangium is two cells 



