INTRODUCTION. 271 



vol. ii.), who described the following seven species of this genus: 

 Sacch. cerevisice, Meyen (seep. 114, vol. ii.); Sacch. ellipsoideus, 

 Reess (see p. 114, vol. ii.); Sacch. conglomeratus, Reess; Sacch. 

 exiyuus, Reess ; Sacch. Paslorianus, Reess (see p. 116, vol. ii.) ; 

 Sacch. mycoderma, Reess ; and Sacch. apiculatus, Reess. Of these, 

 however, only one, viz., Sacch. apiculatus, has been since identified 

 with certainty. Reess did not act consistently in this matter, 

 since, as he himself pointed out, this species does not produce 

 endospores, and therefore should not have been placed with the 

 Saccharomycetes, which he expressly declared to be characterised 

 by endosporulation. He describes this budding fungus (for which 

 see chap. Ixi.) as consisting of " lemon-shaped cells produced 

 by budding, and provided with short apices at each pole ; average 

 width 2-3 p, length 6-8 ^ ; sometimes elongated as short fila- 

 ments. New buds are formed solely at the apices of the parent 

 cells, and usually detach themselves at once, rarely remaining 

 joined, in short lengths or branching. Ascosporulation not 

 detected with certainty, and assignment to the Saccharomycetes 

 consequently doubtful." 



With regard to Sacch. mycoderma, Reess probably based his 

 description on a mixture of Mycoderma cerevisice or M. vini and a 

 species of Pichia, since he expressly states that the species pro- 

 duces spores, which (see chap. Ix.) the Mycoderma do not. The 

 five remaining species mentioned by Reess were characterised 

 almost exclusively from the form of their cells, thus rendering 

 their identification impossible. 



Most of his contemporaries followed Reess, except C. O. Harz, 

 who rejected all Reess's species but Sacch. mycoderma, on the 

 ground that they were only different forms of beer yeast due to 

 altered nutrition. 



Hansen's researches on classification are closely interwoven 

 witli his work on the biological and physiological sides, and he 

 proceeded consistently from the outset with the assumption that 

 only such yeasts as produce endospores can belong to the Saccharo- 

 mycetes. This conception, the correctness of which was demon- 

 strated in the course of the investigations, was generally accepted 

 and adopted with but few exceptions, chiefly physicians who 

 followed Schlendrian and called all yeasts Saccharomyces, whether 

 they form spores or not. A few other workers also took the same 

 view, SACCARDO (II.), for instance, continuing in 1889 to con- 

 found Saccharomyces and non- Saccharomyces, a plan also followed 

 by J. Schroeter in his work on the Cryptogam Flora of Silesia 



(1893)- 



The characteristics established as the basis of classification by 

 Hansen, and employed in the present work, may "now be briefly 

 described. Among the morphological characteristics he assigns 

 an inferior position to cell form, owing to the extent to which 

 this is affected by external influences, most species exhibiting a 

 VOL. ii. : PT. 2. s 



