252 SACCHAKOMYCETES. 



their behaviour under various conditions, and in particular as to 

 the mode in which they formed ascospores. Evidence was soon 

 apparent that the conjectures which had been made as to the 

 variety of species in this country and abroad were entirely correct, 

 and that the cultures of Saccharomycetes differed considerably one 

 from another, both as to the temperature and time at which spores 

 were formed, and that these variations were of a regular and defi- 

 nite character, and were coincident with well marked changes in 

 the action of the organism on the liquids in which it was cultivated. 

 The skill of the observer enabled him to reduce these facts to a 

 tabulated form with such accuracy that the investigation yielded 

 not merely a means by which the limits of the genus might be 

 ascertained and defined, but a method by which the varieties 

 within the genus might be differentiated on a basis of classification 

 as exact as that afforded by the reproductive organs of the higher 

 Cryptogam ia. 



In the course of time the details of working have been con- 

 siderably modified, the use of slices of potato or carrot as a culti- 

 vation material having been early abandoned in favour of tablets 

 of porous earthenware, of gypsum, and latterly of gelatine, which 

 last is especially favoured as affording a very convenient means of 

 direct microscopic investigation of the growing cells from time to 

 time. 



Several years were employed in these investigations. Other 

 methods — notably, the characteristic indications yielded by the 

 " mother," or " voile,'' as the continental term is, which is formed 

 under suitable conditions by the different species upon the surface 

 of the liquid in which they develop — were employed to confirm the 

 results obtained. The writer has had opportunity to work out 

 these problems as regards three varieties — those described by 

 Hansen as S. Cerevisice I., and S. Pastorianus II. and III.— with 

 the following results, which are sufficiently near to those obtained 

 on the Continent to be considered satisfactory. The production 

 of spores in these three varieties ceases entirely at a temperature 

 above 98^^ or 99° F., and becomes very slow below 55*^ F., ceasing 

 altogether at 35^ F. 



The periods of spore development at 62° F. (which is a con- 

 venient temperature for general working) varies from fifty hours in 



