2 53 Bower . — Imperfect Sporangia in certain 
For comparison with those species of Lycopodium which 
are fertile to their base, it may be recalled that at least one 
Fern exists in which the leaves are all fertile. Prantl 
records ‘ the remarkable fact that in Lygodium subalatum , not 
only are normal leaves fertile to the very base, but also the 
sub-primordial leaves, and even the primordial leaves already 
bear sorophores. So that fully sterile leaves, or primary 
and secondary segments in this species are as yet unknown V 
Now it is to be noted that Lygodium belongs to a peculiarly 
ancient stock, which gives a special significance to the fact 
recorded by Prantl. And here it may be remembered that 
Prantl firmly held the idea of the priority of fertile over 
sterile leaves, and asserted it repeatedly 2 . Though no one 
would now subscribe to his comparison of the Hymeno- 
phyllaceous sorus with the Moss-sporogonium, his other points 
should not for that reason be discounted. But however correct 
his opinions may be, the evidence in the case of Ferns is 
likely to be less conclusive than for Lycopods. For it seems 
to be true that rudiments of sporangia are most frequently 
preserved where the sporangia are borne singly, and make an 
early appearance on the part which bears them, as in the Lyco- 
pods ; while in the Ferns the sporangia are formed relatively 
late upon the sporophyll, and usually in large numbers. 
And here I may remark that the Ferns should not be 
taken as a general guide to the morphology of other Pterido- 
phytes ; they are clearly a very specialized series, and on 
that account have not been put in the forefront of the 
present discussion. The argument derived from comparison 
of species of Lycopodium stands upon its own footing, and 
requires neither support nor check from comparison with the 
larger-leaved Filices, with which they have no near affinity. 
Imperfect Sporangia in Fossils. 
The facts being as above stated for living species of Pterido- 
phytes, the question arises whether there is any similar evidence 
from fossils. It may be said at once that the facts are scanty, 
and the arguments to be based on them inconclusive. 
1 Schizaeaceae, p. 14. 2 Hymenophyllaceae, p. 62 ; Schizaeaceae, p. 6. 
