62 H. MARSHALL WARD. 



fungus of the potato disease) no sexual act has as yet been discovered. 



Another obvious objection may be raised as follows : The Sapro- 

 legnice are in the main saprophytes, and yet they are said to be ad- 

 vanced towards apogamy — parthenogenetic, at any rate. The answer 

 may be that they are saprophytic chiefly on animal protoplasm which 

 contains more potential energy than does vegetable protoplasm. At 

 the same time, some Saprolegnice are parasitic on plants, and S. ferax 

 now appears to be parasitic on fish. 1 



Among the Zygomycetes, again, we meet with parasitic forms in 

 which the very simple sexual organs and process are, so far as we 

 know, as typically perfect as in the other members of the group. 

 The reply here is the same as in the case of the Peronosporece. The 

 Mucors must be an older group than Piptocephalis and others which 

 are parasitic upon them. Hence we may assume that the inherited 

 sexuality is too strong to have been replaced by the effects of admix- 

 ture of the protoplasm of the Mucor, which, moreover, is probably not 

 very different, and can scarcely be considered as provided with more 

 energy. A similar argument may apply to the Lichens. The higher 

 forms are specialised parasites on green Algse, which must be able to 

 supply substances containing great potential energy, and no traces of 

 sexuality are found in them. In the Collemacece, however, where sexual 

 organs occur, the fungus is associated with a very low form of Alga, 

 one of the Cyanopliycece, and appears rather to be feeding upon the 

 diffluent matters around the algal cells, than strictly parasitic on the 

 Alga proper. This is so much the case that, as is well known, some 

 lichenologists have doubted whether to rank the Collemacece with 

 Lichens at all ; and all observers must agree that it is difficult to 

 decide when a mass of Nostoc is to be regarded as all Alga or passing 

 into the state of Collema. I remember cases in my time at Cambridge, 

 when I observed patches of Nostoc on the roadside at Shelford, and 

 patches of Collema some distance away. At points between, there 

 were patches of Nostoc in various stages of transition between the two. 

 In Ceylon, again, I have observed masses of Rivularia with fungoid 

 hyphee associated at least as definitely as in these cases, and the same 

 occurs in masses of Gloeocapsa in greenhouses. I do not attempt or 

 wish to cast a doubt on the lichen character of the Collemacece ; I 

 merely point out that, as in the case of other parasitic Fungi, the 

 Ascomycetes of the Lichens exhibit gradations of parasitism from mere 



1 Prof. Huxley, loc. cit. 



