500 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



said for the Filmy Ferns, as representing the more primitive 

 forms. 



1. On the general ground that because development has pro- 

 ceeded from the simpler to the more complex, it may be assumed 

 that the comparatively simple HymenopJiyUdcece were the original 

 type, and certain points of similarity to the Mosses strengthen 

 the assumption ; but nowadays everyone knows that degenera- 

 tion in one form or another, resulting in simplification, is not 

 uncommon, and most parasites, or any aquatic Phanerogam, 

 might serve as an example to show that this assumption is un- 

 trustworthy, unless it be supported by strong evidence. 



2. Let us then examine the evidence by comparison of the 

 Hymenophyllacece with the Mosses. The chief points of simi- 

 larity are : — 



(i.) The filamentous, protonema-like prothallus. 

 (ii.) The projecting sexual organs, 

 (hi.) The presence of single, well-defined apical cells, 

 (iv.) The filmy character of the leaf. 



The last of these may be at once dismissed ; it is obvious that 

 the filmy leaf of the Hymenopliyllacece is a part of the sporo- 

 phyte, while the so-called leaf of the Moss is part of the game- 

 tophyte ; the two are not homologous parts, and accordingly the 

 comparison cannot be looked upon as convincing. Moreover the 

 " filmy " character is not restricted to any one division of the 

 Ferns ; it appears in the Asplcniums and Todeas as well as in 

 the Hymenojjhyllacece, and therefore we have every reason to 

 believe that it is a character of adaptation to a moist habitat, 

 which may be assumed at distinct points in the system, in which 

 case the similarity of the Moss-leaf and that of the Filmy Ferns 

 might also be viewed as a similar adaptation rather than as a 

 token of affinity. 



The presence of a single apical cell at the apex of the young- 

 Moss sporogonium, and also at the apex of the stem, leaf, and 

 root of the Leptosporangiate Ferns, while such are absent (or 

 less definite) in the Eusporangiate Ferns, is certainly a fact 

 worthy of note ; and the common presence of single initial cells 

 in the lower forms, and their absence from most Phanerogams, 

 may be regarded as pointing towards the conclusion that the 

 former are the lower in the scale. Examples are, however, known 



