FILTCALES 



^ t T 

 .l.-ll 



vascular arrangement in the leaves of Ferns resembles that in 

 Flowering Plants more nearly than does that of their stems. 



For the study of the tissues composing a vascular strand, a rhizome 

 with long internodes, such as the Bracken, gives the best results. In 

 a transverse section taken between the leaf-insertions an outer and 

 inner series of vascular strands is found, separated by an incomplete 

 ring of sclerenchyma. The outer series corresponds to the mesh-work 

 of Nephrodhmi, the inner are accessorv, or medullary meristeles 



Fig. 270. 

 Part of a traaia^-crsc section of a nieristele of Bracken. ,§ = ground parenchyma, 

 tf— endodemiis. _^/i=phloem with sieve-tubes. .rv = xyleni, witti lar.cc scalarifonn 

 tracheides. Some smaller traclieides lying centrally are the proto-x\'ieni. ( x 75.) 



(Fig. 269). Each one is circumscribed by a complete endodermis. This 

 is usual in Ferns. Each consists of a central core of xylem, surrounded 

 b)' phloem ; in fact they repeat the main structure of the protostele 

 itself. A small part of one of them, examined under a high power, 

 gives the following succession of tissues (Fig. 270). Passing inwards 

 from the starchy ground-tissue, with intercellular spaces [g], the layer 

 of brownish cells of the endoder)nis (c) forms a continuous barrier, de- 

 limiting the strand sharply. Within it follows the pericyde, with its 

 cells not verv regularlv disposed, but corresponding roughlv to the 

 cells of the endodermis, both having been derived by division from a 



