io6 MORPHOLOGY AND LIFE-HISTORY OF YEASTS. 



of the yeast cell from lifeless material could no longer be 

 claimed with certainty, there was a probability of yeast being 

 evolved from lower fungi on the one hand, and into higher 

 fungi on the other. 



Two circumstances favoured the inception of this opinion 

 and prolonged its existence. One of them consisted in the 

 lack of positively reliable pure-culture processes for enabling 

 the observer to start with a single individual (in this case a 

 single cell) and trace its development with uninterrupted super- 

 vision, to the exclusion of all other germs. It would be setting 

 too small a value on the circumspection of the workers in 

 question and the adherents of the assumption that yeast is 

 descended from other fungi, wei'e one to suggest, in their 

 justification, that they were not even dimly aware of the 

 indispensable character of such a condition. They must there- 

 fore have recognised that their method of working was un- 

 reliable and led to deceptive results, and must have been 

 inwai'dly convinced that the solution of this problem was the 

 next task to be attempted. We have to reproach these ex- 

 perimenters that they did not follow this inevitable knowledge 

 to its conclusion, and did not devote their whole energy to 

 first elaborating a truly reliable method of working. This we 

 must do because the confusing results they conjured up by 

 the aid of their oflicious culture methods, inflicted a twofold 

 injury to science : first by aggravating the task of real research, 

 and then by casting over the final results of the latter an 

 anticipatory shadow of depreciation, which is solely due to these 

 mycological necromancies. 



The second circumstance favourable to the endeavours of 

 those who tried to show the descent of yeasts from other fungi 

 was the discovery of pleomorphism by Tulasne. Since the 

 year 1851, this worker demonstrated, by a number of examples, 

 that certain of the higher fungi were capable, under difi'erent 

 conditions of nutiition, of assuming different forms ; e.g. at 

 one time appearing as a mycelial thread and putting forth 

 conidia, at another as a sclerotium fiom which proceeded small 

 pileated fungi. With such an instance we shall become 

 acquainted, in the case of Sderotinia Fuckeliana, later on. In 

 fact, in other words, it was thereby proved that many of the 

 living forms which had hitherto been regarded as separate 

 species of fungi, merely formed a phase in the cycle of develop- 

 ment of one and the same species of fungus. This theory 

 of pleomoi'phism — ^^which the inquiring reader will find fully 

 described in the mycological handbooks already mentioned, 

 more particularly in the treatise of A. Gilkinet (I.) recom- 

 mended by A. de Bary — was established on an unassailable 

 basis by its founder, by careful investigations of particular in- 

 stances, and really marked a new epoch : not merely in mycology 



