362 Bower. — A Theory of the 
sterile tissue projecting upwards into the sporangium, though 
more efficiently in the Psilotaceae by formation of complete 
septa. But the septation which is there seen in a minor 
degree becomes a more prominent feature in the Ophio- 
glossaceae, a family which on general grounds of comparison 
of both generations I believe to be allied to the Lycopods. 
I cannot here enter into details of the evidence (see Phil. 
Trans. 1894), suffice it to say that I still consider the facts 
sufficient to support the conclusion advanced some years ago : 
that septation has resulted in the production of the fertile 
spike of Ophioglossum from a sporangium of Lycopodinous 
type. The other genera Botrychium , and Helminthostachys 
may be regarded as showing further steps in the separation 
of distinct sporangia, the latter exhibiting also an eruption 
of sporangiophores, laterally on the fertile spike : a repetition 
in fact of the same process as we have recognized in the origin 
of the strobilus itself. This great elaboration of the body 
which appears to correspond to the Lycopodinous sporangium, 
marches parallel with the increase of the subtending sporophyll : 
in this series, which I believe to be an advancing series, I think 
we may thus see how characteristically large-leaved forms, 
with relatively few leaves expanded in slow succession, may 
have arisen from strobiloid forms with numerous small leaves. 
This leads to the third large series of Pteridophyta, viz. 
the Ferns : I think it not improbable that they, with their 
large leaves and numerous sporangia, originated from some 
smaller-leaved strobiloid ancestry. On grounds already 
explained elsewhere (Annals of Botany, Vol. V, p. 109) 
I have concluded that the Eusporangiate Ferns were probably 
the more primitive, and of these perhaps Danaea the most 
so. It is not difficult to understand how, on a hypothesis of 
septation of sporangia spread out over the surface of an 
enlarging sporophyll, the peculiar sorus of that Fern might 
originate : from such a type, by divers methods of isolation 
of the sori, and separation of the sporangia, the various forms 
of Leptosporangiate Ferns may have been derived. So far 
then from accepting the latter as the primitive types of 
