114 THE BOTANICAL MAOAZmE. IVoi. xxxv. No. 4t6. 



we discuss tlie case with leaf-gaps, putting aside the type with per- 

 foration or dissection for a moment, it may be considered that the 

 dictyostele is derived from the solenostele by the overlapping of foliar 

 gaps. As to the process of the overlapping Gwynne-Vaughan^' says, 

 "it appears that two different factors may be concerned in bringing 

 about this overlapping of the leaf-gaps. In the first place it is evident 

 that if the leaf-gaps remain open long enough after the departure 

 of the leaf-traces, they will evidently overlap ; again, the same result 

 will also be obtained if the leaves be crowded sufficiently close 

 together, although the leaf-gaps may close up comparatively rapidly." 

 In a word, he considered two factors — the prolongation of foliar 

 gaps and the shortness of internodes. These factors were also adopted 

 by Tansley^^ as correct. If this view is correct, the intermediate types 

 between the two vStelar forms may be found. In fact, there are many 

 such intermediate or transitional types.^^ 



Next, the form and the relation of rhizomes and leaves in Polypo- 

 diaceae will be considered. There are two extreme forms of rhizomes, 

 one creeping and the other erect. In general, leaves in the former 

 are arranged loosely on the rhizome, while in the latter the arrange- 

 ment of leaves is so crowded that the rhizome forms, with petiolar 

 bases, a bulb-like mass. The distinction between these two forms, 

 however, is not absolute, because they are not only connected by 

 many intermediate ones, but also are variable in the different parts 

 of one and the same individual. In this respect, Diels''^ says that, 



•'das kriechende Rhizom besitzt Internodien von verschiedener Lange, 



ventral angefiigte Wurzel und dorsal meist zweizeilig, sehr selten 

 einzeilig angeordnete Blatter. Das aufsteigende oder aufrechte Rhizom 

 zeigt meist stark gestauchte Internodien und dichte spiralig gestellte 

 Blatter." Accordingly, gaps may be said to overlap in the erect 

 rhizome with crowded leaves, but this is very doubtful in the case 

 of the creeping one with loosely arranged leaves. On this point, 

 Gwynne-Vaughan^^ says, on the solenostelic ferns, that "all these 

 (solenostelic) ferns have a creeping, more or less dorsivcntral rhizome 



1) Gwynne-Vaughan, I.e. '03, p. 694. 



2) Taksley, I.e. p. 187. 



3) Gwynne-Vatjqhan, I.e. '03. 



4) Diem, L. (1902) Polypodlaceae, in Engler's Pflanzenfamilien, I Tell, Abt. 

 A (Pteridophyta). s. 143. 



5) Gwynne-Vaxjghan, I.e. '03, p. 691. 



