120 NUMAD FUNGI. 



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 Fucacese or 

 Bladder-wracks of our sea-coasts, and in Volvox, the Desmidiese, 

 the Diatomacese, and other Algre, 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 reprodiictive 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 reduced itself to this 

 diificulty — 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 

 Oscillatorieae. 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 

 seed when the vigour of its growth is ceasing. I need only remind you 

 that a rapidly-growing fruit-tree, in which a superabundance of sap is 

 present, seldom fruits ; and that a gardener who wishes to make a 

 geranium flower stints its supply of water. It is true that there is a 

 seeming exception to this law in the case of trees which flower in 

 spring, before the leaves are out ; the common Coltsfoot (l'ussila()o) 

 would also seem to contradict the rule ; but really they obey it. In all 

 these cases the buds which are to develop into the flowers are formed 

 at the doge of growth in autumn and only wait till spring to complete 

 their development. Applying these considerations to the Uredinece, 

 we are naturally led to look for the sexual process in the production 

 either of the Puccinia or of the CEcidium. The probability is vastly 

 in favour of the latter, \iz : that fertilisation occurs in the mycelium 



