80 
NOMAD FUNGI. 
cearum, but why not all? This is a question upon which I have seen 
few attempts made to throw any li^^ht. We can see the object of the 
Uredo and the Puccinia, but not of the (Ecidium. There is only one 
glimmer in the darkness, and that will be introduced by the point to 
which I wish now to draw attention. I believe that in the life-history 
of most plants there must occur, more or less frequently, a process 
akin to the fertilisation of the phanerogams. There must be that 
mysterious commingling of the contents of two distinct cells, from 
which animal and vegetable species alike derive a renewed lease of life. 
Many facts point to the conclusion that a species which reproduces 
itself only by budding has a tendency to degenerate continually, and 
finally to become extinct. It is true that there are apparent (or real) 
exceptions to this law, where a species maintains itself, so far as we 
know, by purely asexual means. But it seems to me that we 
lose the significance of a whole body of facts if we refuse to 
believe that the law is as I have said. We cannot forget in how 
many instances the presence of an act of fertilisation has been 
detected where it was formerly unknown, as in the Fucaceaj or 
Bladder-wracks of our sea-coasts, and in Volvox, the Desmidieae, 
the Diatomaceae, and other Algae, not to speak of instances now so 
well known as the Ferns and the Mosses. There are now several 
groups of Fungi in which a true reproductive process is known to 
occur, as in the Mucorini, the Peronosporeae, the Saprolegnieae, and some 
of the Ascomycetes. We must remember that the reproductive pro¬ 
cess is one of the chief means, on the Darwinian theory, by which new 
species are produced; a group of organisms, which has entirely lost 
traces of a gamogenetic act, has thereby I’educed itself to this 
difficulty—that as the existing species disappear, under the influence 
of competition, it can form no others of a more or less divergent 
character to suit the changing circumstances, and so has doomed 
itself to a sure, though lingering, death. It is true that, if it avail 
itself of the sexual act to produce invigorated descendants, it per¬ 
petuates itself under a changing form, which finally becomes what we 
call a distinct species; but still it does perpetuate itself, which is the 
main point. I believe that the only cases, in which it may be conjec¬ 
tured from our present knowledge, that gamogenesis is absent, are 
found in organisms which inhabit water: such are, perhaps, the 
Oscillatoriese. But it is conceivable that most species which live in 
water are not subject to such changing conditions, do not require 
therefore so great a power of adaptation to circumstances as do those 
which live in the air. However this may be, a family of plants so 
large and so varied as the Fungi are must have formerly possessed the 
means of sexual reproduction, and probably in great part still retains 
it; in no other way can the existence of numerous and closely-related 
species be accounted for. 
Now, if we were to look for a process of fertilisation in our leaf- 
fungi, where should we probably expect it to occur ? Analogy will 
help us to answer this question. A flowering plant usually produces 
