the more primitive type in the Ferns ? 1 1 3 
suggestion as to the origin of the Fern from the Moss-sporo- 
gonium. The above brief statement will serve to show how 
long and how consistently the opinion has been held by 
special writers upon the Hymenophyllaceae, that they are the 
most primitive types of living Ferns. We will now consider 
wherein the points of similarity between them and the Mosses 
really lie, and try to estimate them at their true value in sup- 
port of the primitive character of the Filmy Ferns. 
Over and above the corresponding facts of alternation in 
the Mosses and Filmy Ferns, and the homosporous charac- 
ter which they both share, the chief points of similarity are 
these : — 
(i) The filmy character of the leaf ; 
(ii) The filamentous prothallus ; 
(iii) The projecting sexual organs ; 
(iv) The presence of a single, well-defined apical cell ; 
(v) The reputed absence of roots in some Filmy Ferns. 
Each of these will be successively discussed and criticised. 
(i) It was perhaps the filmy texture in the leaf more than 
any other character, which suggested the affinity of the Filmy 
Ferns to the Bryophyta : long before the phenomena of anti- 
thetic alternation 1 were properly apprehended, it was pointed 
out that a similarity of structure exists between the fronds of 
the Hymenophyllaceae and the leaves of the Mosses, since in 
both cases the filmy leaf may consist of only a single layer of 
cells. But while such a comparison was not unnatural some 
fifty years ago, it is to be borne in mind that the facts of 
antithetic alternation are now clearly before us 1 : that we are 
comparing the filmy leaf of these Ferns, which is part of the 
sporophyte, with the so-called leaf of the Moss, which is part 
of the gametophyte : the two are not strictly homologous 
parts, and accordingly their comparison cannot be accepted 
as convincing : at best we have here only an analogy, the leaf 
of the Fern not being the lineal descendant of the leaf of the 
1 In case this term be unfamiliar, reference may be made to an article ‘ On 
antithetic as distinct, from homologous alternation of generations in Plants,’ 
Annals of Botany, vol. IV, p. 347. 
