54 H. MARSHALL WARD, 



and parasite are used somewhat loosely. This being admitted, it 

 may happen that further knowledge will strengthen the connection 

 spoken of. 



We are at least assured that profound differences exist — in degree, 

 at any rate — between the saprophytism of a Mucor growing in a 

 solution of horse-dung, and of a Pythium developing its fructification 

 in the rotting parenchyma of a plant which it has previously killed. 



There is also an equally striking difference between the parasitism 

 of an epiphyte like Frysiphe and that of a highly-specialised iEcidio- 

 mycete like Puccinia. But I would insist upon more than this. It 

 is not only in the mode of attacking or living upon the substratum 

 that one fungus differs from another ; differences as to the kinds and 

 quantities of the various matters absorbed must also exist, and a 

 Uredine in a leaf no doubt obtains different food (and in a different 

 way) from that taken by Claviceps in a grain of rye, or Ustilago in a 

 hypertrophied swollen stem of Zea Mays. That these differences may 

 be very important — though we do not know exactly in what they con- 

 sist — is fully demonstrated in cases of heteroecism. 



I have already pointed out that the coexistence of apogamy (or the 

 total suppression of sexual organs) and parasitism is noticeable espe- 

 cially in the highly specialised parasites. In forms which, like the 

 majority of the parasitic Peronosporece and Zygomycetes (e.g. Pepto- 

 cephalis), are nevertheless provided with sexual organs, which, so far as 

 we can see, are quite like those found in the saprophytic forms, we 

 have two points to notice. First, these forms are close to the parent 

 stock in phylogeny — i.e. they are not much modified from the type 

 of Pythium itself, which (as a comparison with Vaucheria shows), is 

 no doubt derived from algal ancestors, and with strongly inherited 

 sexuality. Secondly, such forms are probably not so highly parasitic 

 as is commonly supposed. I do not mean to say that their living- 

 hosts are not robbed by them ; but it is significant that the Peronos- 

 porece are often saprophytes, and that even the most parasitic forms 

 break down the parenchyma of the hosts to a rotting, fetid mass, on 

 which they then flourish. Moreover they are aided by bacteria in 

 this process. In addition to this they are apt to be omnivorous. I 

 have cultivated Pythium De Baryanum 1 on the most various sub- 

 stances, as well as on more than a dozen widely different living plants. 

 In all these cases the parasite appears to flourish in a variety of 



1 Cf. also Do Bary op. cit., and 'Quart. Journ, Mic. Sc.,' 1883. 



