Variations of a Saeeharomyces. By O. F. Dowdesivell. 17 



Within twenty-four hours, at the temperature of the room — 

 about 60° Fahr. — the cells were found to be in active prolifera- 

 tion, and they had multiplied three or four times, principally by 

 gemmation ; some few, however, were already forming hyphae, in 

 some cases having first or simultaneously developed buds ; these 

 hyphae were already three or four times as long as the mother- 

 cells, containing refractive granules, and becoming segmented. 

 Shortly afterwards the occurrence of fission and the formation of 

 endogenous spores was observed, the growth being still confined 

 to a comparatively small spot towards the centre of the shde. 

 These spores are ultimately set free, develope and proliferate as 

 the parent cells. 



It may be readily observed that the cells nearer the groove 

 and more freely supplied with air, are larger than those in the 

 interior of the cell, they look more robust, and the spores, which 

 sometimes amount to a dozen or more in a single ceU, are remark- 

 ably large and well defined ; in this situation, too, the hyphas in 

 some few cases are remarkably long, extending over a considerable 

 portion of the cell — i.e. some mm. in length — passing through 

 the air of the groove, and continuing to grow in the oil on the 

 outside of it. No aerial hyphae, however, are formed. 



Nevertheless, although an ample supply of air does favom- the 

 development of certain phases, yet in the same spot of the same 

 nutritive medium, and apparently under, in every respect, precisely 

 similar conditions, all these phases of development occur; and 

 though the cultivation did not originate in a single cell, I do not 

 think it is possible that difierent species were present. In most 

 samples of brewer's or commercial yeast it is easy to detect foreign 

 spores under the Microscope, but that was not so in this case ; 

 and it appears to me that we have here different forms of develop- 

 ment, not owing to differences of external conditions, but to an 

 inherent tendency to variation or sport, affording a confirmation of 

 the Darwinian doctrine, that of the two factors which determine 

 the liability of living organisms to variation — viz. the nature of 

 the organism and the nature of its external conditions, the former 



This, which I have found very useful and perfectly adapted for continuous obser- 

 vation of development with the highest powers, is merely a slight modification of 

 a form long since used and described by, I think, Brefeld, and which I was 

 myself in the habit of employing formerly. As I found great difficulty recently 

 in getting them constructed, I may mention that those I now use are well and 

 accurately made by Messrs. Beck. The " hanging drop " so frequently used in 

 these cultivations, has some great and obvious disadvantages, the organisms in 

 the lower part of the drop cannot be brought into the focus of a high power 

 unless the drop is very minute, when it is liable, in spite of precautions, to be 

 dissipated by evaporation ; and again, unless the nutrient medium is viscid the 

 preparation is apt to be spoiled, if the shde is tilted, by contact with the walls of 

 the cell and the oil. 



Ser. 2.— Vol. V. C 



