278 



PLAGIOGYRIACEAE 



[CH. 



Vol. I, p. 149. Roots arise with some degree of regularity right and left of 

 the departing leaf-trace, each with a sclerotic sheath. 



The anatomical similarity of these features to what is seen in the more 

 advanced types of the Osmundaceae cannot be missed. If allowance be 

 made for the larger number of more closely disposed leaves, together with 

 a different distribution of the sclerotic tissue, the primitive dictyostelic ring 

 of Plagiogyria closely resembles the still more primitive dictyoxylic ring of 

 Osjiiujida cinnamoniea, where there is also an iimer endodermis and phloem, 

 A B 



Fig. 544. A , transverse section of the stem of Plagiogyria pycnophylla, showing sclerenchyma black , 

 vascular tissue shaded. ( x 2.) B, tangential section of leaf-bases, one of them [st) converted into 

 a stolon. (Natural size.) C, a dichotomy in P. semicordata, showing steles, leaf-traces, and 

 sclerenchyma. ( x 2A.) D, transverse section of a solenostelic stolon of P. pycnophylla. ( x 4.) 

 E, base of a petiole oi P. pycnophylla, showing pneumatophores (/>). (Enlarged.) 



and the protoxylem is mesarch as in Plagiogyria {com^dire. Fig. 126, Vol. l). 

 One point of difference is that in O. cinnamoinea the inner endodermis does 

 not connect with the outer at the xylic gaps, though it does at the "ramular 

 gaps": in Plagiogyria connection is made at each foliar gap. This, however, 

 is found to occur, though irregularly, in the large Osmundites Carnieri, if as 

 is believed the line of delimitation of the stele in that Fern is really endo- 

 dermis (Vol. I, Fig. 127). The similarity extends in structure, but not in 

 outline, to the leaf-traces, though those of Plagiogyria show at their first 



