CYATHEAE 



607 



by a diagrammatic figure (Fig. 338), but with the reservation that the rapidity 

 with which the successive stages are passed through varies considerably : it 

 is believed, however, that the diagram will serve to represent the course 

 of development of the vascular system, not only in the Cyatheae, but also 

 in most of the solenostelic and dictyostelic Ferns, up to the particular 

 stage that they retain when mature. The following description is taken 

 almost verbally from Mr. Gwynne-Vaughan's memoir. 



The young plant of Alsophila excelsa has its leaves arranged radially 

 all round the axis. At the very base of the stem the single central 



FIG. 337 C. 



Cyathea Itnrayana, Hook. Pieie of stem with four leaf-bases, after removal of the 

 outer layers of cortex, seen from without. The margins of the four leaf-gaps, the bundle? 

 which spring from them and pass into the leaves, the roots inserted on them (black), and 

 the bundles which run down within the cortex are exposed. The cortical bundles and 

 root bases are quite free, the rest are covered by semi-transparent parenchyma. Natural 

 size. (After De Bary, from Engler and Prantl, Xat. Pflanzenfatn.') 



cylinder possesses a small central strand of xylem, usually with a few 

 xylem-parenchyma cells intervening between the tracheides. The first leaf- 

 trace may depart without in any way altering the structure of this stele, 

 or of its xylem-strand, but usually the phloem on the adaxial surface of the 

 leaf-trace is prolonged a short distance downwards into the substance of 

 the central xylem. At the departure of the subsequent leaves this feature 

 is much more pronounced, and the phloem thus decurrent runs down 

 through the whole length of the internode to meet with that decurrent 

 from the leaf below. In the second leaf, however, it often falls short of 

 the point of departure of the first leaf, and ends blindly in the internode. 



