1 (5 Transactions of the Society. 



II. — On the Occurrence of Variations in the Development of 

 a Saccharomyces. By G. F. Dowdeswell, M.A., F.L.S., 

 F.KM.S., etc. 



(//cfi'Z IQth December, 1884.) 



The occurrence of pleomorpLism in some of the higher fungi 

 lias heen well established, and is generally accepted. In some 

 cases, no doubt, the instances of asserted variations of form arise 

 from erroneous observation, from the occurrence of contaminations, 

 with the presence of different species in the cultivations ; this has 

 given rise to exaggerated views, so that the doctrine of pleo- 

 morphism has been extended to an extravagant length, as de 13ary 

 justly terms it.* 



In regard to the Saccharomycetes, the observations asserting 

 that yeast {S. Cereviseae) is but the conidial form of Penicillium 

 glaucum are well known ; the development of branching hyphae 

 and endogenous spore-formation have been already described ; but 

 these form- variations have always been considered to be deter- 

 mined by external conditions, such as a difference in the nutrient 

 medium, the exhaustion or insufficiency of which has been thought 

 to occasion the formation of spores. 



In cultivating some forma of fungoid blight lately, I observed 

 the occurrence of innumerable cells of a species of Saccharomyces ; 

 it is one which I cannot exactly identify with any previously 

 described. A growth of this is shown in the cultivating cell 

 under the Microscope. In this it will be seen that development 

 occurs both by means of gemmation, by fission, the formation of 

 a mycelium with a slight tendency to branch, and also by endo- 

 genous spore-formation. 



The nutrient fluid is here a 10 per cent, solution of cane sugar 

 with the small proportion of mineral salts present in tap-water. 

 In this it developes much more freely than in other solutions 

 such as Cohn's fluid, or vegetable infusions. To originate the 

 cultivation, as small a quantity of the cells as could be taken on 

 the point of a platinum needle was placed on the centre of the 

 slide ; there were about a score, not many more, and they could 

 be easily counted and examined individually under the Microscope. 

 Over these, with a droplet of the solution, was j)laced the cover- 

 glass, closed by oil round its margin, the groove in the slide 

 aflbrding a supply of air to the cultivation.! 



* Vergleich. Morpliol. u. Biol, der Pilze, &c., 1884, p. 136. 



•]• The form of cill used is a plate-glass slide J3 by 1 in. and 1/10 in. thick. 

 In this a circular groove is cut 1/10 in. wide and ]/20 in. deep ; the centre stage, 

 G/10 in. in diameter, is countersunk 2/1000 in , but it may be either level or sunk 

 1/1000, 2/1000 or 4/1000 in. to suit the size of the micro-organisms cultivated. 



