1 1 6 Bower,— Is Eusporcmgiate or Leptosporangiate 
conformation of the sexual generation, in view of the extent 
of the direct impress of external circumstances upon it in 
certain known examples 1 : at the same time I am free to 
admit that a reasonable case (though not a demonstration) 
can be made out for the relatively primitive character of the 
Moss-protonema, notwithstanding that the formation of a pro- 
tonema is not a constant phenomenon in all Mosses 2 . 
Passing to the second question, viz., whether the similarity 
of form between the protonema of the Moss and the fila- 
mentous prothallus of the Hymenophyllaceae is an indica- 
tion of real affinity, we enter on different ground. Between 
the Mosses and the Ferns there is a very wide gap. Though 
the general facts of alternation are similar, still as regards the 
form and structure of the sporophyte the two families have 
virtually nothing in common ; but in the general conformation 
of the prothallus, and in its propagation by gemmae, they are 
alike : can this be accepted as an index of affinity in face 
of so fundamental a difference in the neutral generation ? 
Among the higher plants it is notorious how little attention is 
paid to similarities of external conformation of the vegetative 
organs if the other characters indicate strong divergence, and 
there is no reason why this principle should be neglected in 
dealing with the Cryptogams. Moreover in the protonematoid 
growths of the Hymenophyllaceae we see an excessively in- 
constant character : even within the genus Trichomanes , while 
the prothallus of T. pyxidiferum is throughout filamentous, 
with exception of the archegoniophores, that of T. alatum 
is most diverse in its form 3 : in Hymenophyllum on the 
other hand the flattened form is prevalent : thus within the 
Hymenophyllaceae there is great want of constancy in that 
very character to which, in accordance with current views, so 
much importance is attached as evidence of relationship to the 
Mosses. This is in itself sufficient to cast doubt upon it, 
1 Annals of Botany, vol. I, p. 292. 
3 Andreaea is an exception. See Berggren, Studien ofver Mossornas bygnad och 
Utveckling (Lunds Univ. Arsskrift. T. VII). 
3 See Annals of Botany, vol. I, Plates XIV, XV. 
