FILICALES 



are finely scalariform, and are scattered round the periphery of the xylem- 

 core, which is itself composed of tracheides, intermixed with parenchyma 

 (Fig. 306). The petiole is traversed by a single strand, which comes off 

 from the protostele with only superficial disturbance of it : in fact the 

 mature plant maintains the simple relation of the protostele and trace 

 which is seen in its seedling (Fig. 307). The foliar strand in the climbing 

 petiole is an almost cylindrical body, with bays of phloem protruding 

 into the xylem : it is probably a derivative form of the more usual flattened 

 type, contracted in accordance with the climbing habit. In Schizaea the 

 obliquely ascending or erect stock shows a medullated stele : endodermal 



FIG. 306. 



Transverse section of the rhizome of Lygodium dichotomum. 

 ph = phloem; x = xylem. (After Boodle.) 



6'=endodermis 



pockets are often present at the nodes, or an isolated internal endodermis 

 is occasionally seen, but no internal phloem. Internal tracheides occur 

 in the medullary region, sometimes isolated, sometimes almost bridging 

 across the central pith (S. molluccana). It has been clearly demonstrated 

 that as the stele in the seedling expands, no internal phloem appears : 

 these facts favour a theory of amplification of the stele in Schizaea rather 

 than one of reduction. In Aneitnia Phyllitidis and most other species, 

 as also in Mohria, the mature stem is dialystelic, having a hollow reticulate 

 vascular cylinder similar, except for the leaf-traces being only a single 

 strand, to that of Nephrodium filix mas : each mesh is a leaf-gap and the 

 leaf-trace is inserted at its base. But in A. mexicana and other creeping 

 species the dialystelic state is replaced by closed vascular ring or solenostele. 

 The simpler type of Lygodium is probably the more primitive, and as 



