272 CLASSIFICATION OF SACCH ABOMYCETACE^. 



large number of cell forms (see p. 1 16, vol. ii.). In fact, it is only 

 under definite conditions of culture that the cell form can be 

 utilised as a characteristic of species. Unfortunately, there are 

 still botanists who call all large rounded cells /Sacch. cerevisice, all 

 small oval ones Sacch. ellipsoideus, and all elongated cells /Sacch. 

 Pastorianus, and thus keep to the same standpoint as Reess. The 

 shape of the spores and the production of films are important 

 generic characteristics, and in some cases of species as well. 

 Physiological characteristics are of great importance in classifica- 

 tion, especially the critical temperatures of budding, film produc- 

 tion, and sporulation (see table opposite p. 136, vol. ii.); and also 

 the behaviour of the species toward different sugars (see chaps. Ixiv. 

 and Ixv.), large quantities of yeast and pure sugars being essential 

 for this purpose. In this instance a macroscopical examination is 

 necessary, microscopical tests not affording sufficient accuracy. 

 The yeast is sown in yeast- water containing 5 to 15 per cent, of 

 the sugar in question, and the production of alcohol is tested for. 

 Finally, Hansen employed as a means of differentiation the macro- 

 scopic appearance of the vegetations on different solid nutrient 

 media. His methods differ essentially from those of Reess by 

 being entirely of an experimental character, and it follows there- 

 fore that the value of the results for purposes of comparison 

 depends on the experiments being carried out under identical 

 conditions. 



Lindner employs the appearance of the giant colonies as a 

 specific characteristic ; and Will has also done good work in the 

 study of these forms. 



The fermentative habit (as top or bottom yeast) has no longer 

 the same importance as a means of classification that it formerly 

 enjoyed, on account of Hansen's recent investigations in this con- 

 nection (see p. 264, vol. ii.). 



Even many of the species put forward as new during the past 

 few years are described in such an imperfect manner that they 

 cannot be included in our classification, the reason in many cases 

 being that the newly discovered species have shown the description 

 of the older ones to be insufficient. An example of this kind is 

 afforded by H. Lindner's so-called Sacch. hyalosporus, which is 

 characterised by the production of bead spores. This peculiarity, 

 however, is shared by several other species, and consequently a 

 more complete description is necessary before the species can be 

 identified. Other workers, again, have named species without 

 describing them ; and these we are therefore compelled to omit, 

 confining our list to such species that have been so fully described 

 as to render identification feasible. Unless specific mention is 

 made to the contrary, the description in each case is that fur- 

 nished by the discoverer of the species. The source oi information 

 is quoted in each case. 



A few preliminary notes of explanation will facilitate clue 



