THE PTERIDOPHYTA : FILICALES, THE FERNS 535 



together the various vascular rings into a three-dimensional lattice, also by 

 the departure of very numerous leaf traces from the outer vascular zone, 

 and by the multiplicity of adventitious root traces which come from the outer 



Fig. 532. — Marattia fraxinea. Very young plant showing 

 stipules attached to leaf bases. Natural size. 



and inner zones (Fig. 533). In spite of this it is recognizably a compound 

 dictyostele of the Pteyidium type, differing only in the much greater degree 

 of dissection of the stele. A noteworthy peculiarity is the absence of an 

 endodermis, except in the young plant. 



The commissural strands appear to be downward continuations of the 

 incoming leaf-trace bundles. Each of them leaves the outer stele at the top 

 of the leaf gap directly below that to which the commissural strand belongs, 

 and it enters the inner stele at the base of a similar gap. The gaps in the 

 inner stele may therefore be regarded as true leaf gaps, like those in the outer 

 stele. 



There is ground for believing that the whole vascular system in Marattia 

 is a complex of leaf traces and that no truly cauline stele is present. 



In the development of the young leaf the marginal row of initial cells 

 typical of Leptosporangiatae is replaced by a band of meristematic tissue 

 which is associated with the much thicker leaf blade of Marattia. 



