Classification of the Saccharomycetes. 79 



is only an application of the same principle in the opposite 

 direction. 



It follows (i) that we must consider as a species any 

 form or group of forms which, under present conditions, 

 can be clearly distinguished from all other forms, even 

 though we may know that, if the environment were changed, 

 the species would change too ; and (2) that species must 

 necessarily be of various ranks and of various degrees of 

 definiteness, as indeed we know to be the case. And in no 

 part of the scale of organised beings should we expect to 

 find clearer proof and more frequent examples of this 

 doctrine than among the lower Algae and their derivatives, 

 the lower Fungi. 



In conclusion, it may be remarked that neither Cohn 

 nor Zopf have put forward their rival systems as final. At 

 the time of its promulgation Cohn's first arrangement was 

 indeed the only possible one, but he never asserted that 

 all the forms which he catalogued would be found to be 

 true and independent species. Zopf, on the other hand, 

 does no more than devise a system in which certain newly 

 discovered facts may find adequate representation ; but he 

 does not pretend that it will include all Schizomycetes. 

 The ultimate classification will probably be a compromise 

 between the two, though the exact form which it will assume 

 it is at present impossible to foresee. 



The classification of the Saccharomycetes is in as un- 

 decided a state as that of the Schizomycetes, but in a some- 

 what different way. In this case also there are the two 

 opposing parties one holding that most of the forms which 

 have been described in Chapter II. are independent species ; 

 the other, that they are for the most part only phases of 

 growth of one or a few species ; but the third view, which 



