X FILICINE.-E LEPTOSPORANGIAT^ 321 



of the apical cell of the stem and up to the fifth or sixth, and 

 possibly later the first division of the leaf is dichotomous, and 

 the pinnate form of the later leaves is gradually attained, as in 

 Marattia. As the stem grows its vascular cylinder becomes 

 better developed, and a distinct endodermis becomes evident, 

 and it gradually passes over from the monostelic condition of 

 the young plant to the polystelic form found in the adult. A 

 cross-section of a plant with three fully-developed leaves showed 

 the vascular cylinder to be oval in outline, and consisting of the 

 following parts. A central pith of elongated parenchymatous 

 cells, surrounded by a thick ring of short spiral and reticulate 

 tracheids, outside of which was a zone of phloem, the whole 

 enclosed by a distinct endodermis. The latter is continuous, 

 with the endodermis of the bundles going to the leaves and 

 roots, and the xylem of these also connects with those of the 

 stem bundle. The apex of the stem becomes more and more 

 hidden by the development of scales from the epidermis, which 

 finally completely hide it and form a very efficient protection. 



The petioles of the first three leaves have a single axial 

 vascular bundle, but in the fourth, as in all subsequent ones, 

 there are two. They separate very soon after leaving the stem 

 bundle, which is deeply cleft where they issue from it. These 

 bundles are typically concentric in structure, and have a well- 

 developed endodermis. The number of roots in the young 

 plant exceeds the leaves. In a plant with the fourth leaf still 

 unfolded, there were six fully-developed roots. 



The Mature Sporophyte 



TJie Stem 



The stem in most of the Polypodiacea; is either an erect or 

 creeping rhizome which, unlike that of the Eusporangiats, often 

 branches freely. These branches are always formed mono- 

 podially, and are usually of the same structure as the main 

 axis ; but in 0. struthiopteris great numbers of peculiar stolons 

 are formed that are quite different at first in appearance from 

 the ordinary shoots. The main axis in this species is an 

 upright rhizome about 2 cm. in diameter, but appearing much 

 larger on account of the thick persistent leaf-bases which cover 



Y 



