RESEARCHES ON ASPOROGENATION. 261 



HANSEN (XXXVII.), in 1883, showed that spores can stand 

 greater heat than the vegetative cells. This observation was taken 

 by BEIJERINCK (XXII. and XXIV.) as the starting-point in his 

 endeavours to produce vigorous sporogenation in a culture origin- 

 ally forming only a small number of spores. There is no fixed 

 method for this purpose, the treatment differing with the kind of 

 culture and requiring to be performed tentatively in each case. 

 Beijerinck made the mistake of applying the term regeneration 

 to the result of his experiments, the matter being merely one of 

 selection of the individuals which have not lost their sporogenic 

 power, so that it is incorrect to speak of a lost capacity of the 

 individual. 



We will now deal with Hansen's fundamental experiments, in 

 which he produced permanently asporogenic varieties by the 

 action of certain external agencies, in the same year (1889) in 

 which he observed the spontaneous asporogenic varieties of Sacch. 

 Luiwigii mentioned above. In the course of his experiments on 

 the limits of temperature for budding and sporulation in Saccharo- 

 mycetes, he observed that the maximum temperature for the former 

 function is always a few degrees higher than that of the latter 

 whilst the minimum temperature of budding is a few degrees 

 lower than that of sporulation. This law holds good for all true 

 Saccharomycetes (see pp. 129, 130, vol. ii.). 



Hansen tried to ascertain what happens when Saccharomycetes 

 are grown at temperatures intermediate between the said two 

 maxima and minima respectively, and whether the result is the 

 same in each case. This latter, however, does not occur, the species 

 undergoing a remarkable change on cultivation at a temperature 

 intermediate between the two maxima, though not in the other 

 event. This change consists in the Saccharomyces vegetation 

 completely losing the power of sporulation when cultivated for a 

 number of generations in nutrient liquid at the temperature in 

 question. As might be anticipated, it was also found that the 

 maximum temperature is not exactly the same for all the indi- 

 viduals constituting a vegetation. In experiments for ascertaining 

 the maximum temperature of a species, the result applies to the 

 individuals possessing the highest maximum, though there may 

 be also other individuals present which have a slightly lower 

 maximum temperature. Hence modification experiments may 

 reveal the presence of individuals which apparently can be modified 

 at a temperature below the maximum found for sporulation, 

 whereas in reality these individuals belong to the group exhibiting 

 the lower maximum temperature of the species ; and therefore, 

 even in this case, the modification occurs at a temperature inter- 

 mediate between the maxima for sporulation and, budding respec- 

 tively. Consequently it may be stated, as a general proposition, 

 that the said modification proceeds by cultivation at a temperature 

 bordering on the maximum temperature for sporulation. The 



