534 LIFE-HISTORIES 
bearing sporangia would be a spore-sac-leaf, while the cylindrical 
elongating zone from which it arose would now be a true stem. 
Here would be about as simple a fern as we can imagine; but it 
would have all the essential features, and it is not inconceivable 
that higher forms might have been evolved from it. Suppose, for 
instance, that the sac-leaf member forked into two branches, and 
let one of them be expanded so as to secure as much sunlight as 
possible and be devoted exclusively to photosynthesis, while the 
other branch instead of doing much food-making was narrower and 
developed as many spores as possible from food that the expanded 
branch furnished. Suppose further that the stem lived on from 
year to year, sending new roots into the earth and new leaves into 
the air, then our plant would have become like an adder-tongue 
fern. 
The striking differences between liverworts and ferns of any 
kind have so impressed not a few botanists as to have made them 
doubt the likelihood of ferns having originated in the manner above 
suggested; and this doubt has gained strength from the fact that 
the most ancient fossil ferns are of highly complex organization, 
being often tree-like in form, and so even less like liverworts than 
the presumably degenerate ferns with which we are most familiar 
to-day. Moreover, if modern liverworts are also to be regarded 
as degenerate plants—a view, as we have seen, for which there is 
some evidence—the gap which separates them from ferns is even 
wider. It may well be true that ferns evolved directly from sea- 
weeds in which a clearly marked alternation of generations had 
developed as in certain rather highly organized red alge living 
to-day. On this supposition, however, we are still left with the 
difficulty of imagining the stages through which a seaweed could 
pass in fitting itself for life on land as a tree. Here fossils cannot 
help us, for we have none at all intermediate between seaweeds 
and ferns. Since, however, there are undoubted fundamental re- 
semblances between a Coleochzte, an Anthoceros, and an Ophio- 
glossum, these may offer at least a possible clue as to how the great 
changes in question may have taken place. 
Grape-ferns would be readily derivable from adder-tongues by 
further branching of the two leaf branches, which in the fertile or 
sporangial segment might result in each sporangium being borne 
on a little stalk or branchlet of its own. We may well imagine that 
wonderful possibilities of development lay before such a type as 
this as soon as it established itself on the edges of swamps or on land 
where food and moisture abounded. It could then afford to delay 
the production of spores until it had built a thick, tall stem, by 
means of leaves made larger and larger year after year and devoted 
entirely to making food so that a surplus might be stored in the stem. 
Finally, a very large number of sporangia might be produced upon 
much-branched spore-sac-leaves; and these, held high in the air, 
could scatter their spores most effectively. 
