308 H. MARSHALL WARD. 



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 

 Peronosporese. 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 to have been replaced by the effects of admixture of the proto- 

 plasm 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 Colle- 

 macese, however, where sexual organs occur, the fungus is 

 associated with a very low form of Alga, one of the Cyano- 

 phycese, 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 

 Collemacese with Lichens at all; and all observers must 

 agree that it is difficult to decide when a mass of Nos toe is to 

 be regarded as all Alga or passing into the state of Coll em a. 

 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 hyphse associated at least as definitely as in 

 these cases, and the same occurs in masses of Glceocapsa 

 in greenhouses. I do not attempt or wish to cast a 

 doubt on the lichen character of the Collemacese; I 

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

 Fungi, the Ascomycetes of the Lichens exhibit gradations 

 of parasitism from mere association to highly adaptive para- 

 sitism, where the Fungus has learned (so to speak) to use its 

 host as a slave. 



