SPOROBOLOMYCES 185 



formed at the expense of the culture medium. About two hours 

 after the first spore had been discharged, a second spore began to be 

 developed on the end of the sterigma (Fig. 90, no. 9), and this grew in 

 the normal manner to full size (Fig. 90, no. 10). Then, after the 

 usual interval of time, this second spore was discharged in its turn 

 (Fig. 90, nos. 11 and 12). About an hour and forty minutes after 

 the second spore had been discharged, a third spore began to be 

 developed on the end of the sterigma. This third spore developed in 

 the usual manner to full size and its hilum excreted the usual drop 

 preparatory to spore-discharge (Fig. 90, nos. 13-15). However, 

 owing to some abnormality, doubtless due to the culture conditions, 

 discharge did not take place. 



A number of other yeast cells were observed in which one and the 

 same sterigma produced and discharged two spores in succession ; 

 but, owing to the difficulty of providing suitable conditions for the 

 yeast cells when they are being observed under the high power of the 

 microscope for many hours in succession, the maximum number of 

 spores which a single sterigma may produce was not precisely deter- 

 mined ; but, from the observations just recorded, we may conclude 

 that a healthy S. roseus yeast cell growing under good conditions 

 normally produces on a single sterigma not one spore only as Kluyver 

 and van Niel 1 supposed, but two, three, or possibly four or more spores. 



In the Hymenomycetes and the Uredineae my own observations 

 have convinced me that only one spore is produced on each sterigma 

 and that, in the Hymenomycetes, a basidium-body, along with the 

 four sterigmata, collapses within 20-30 minutes after the moment of 

 discharge of the last of the four spores 2 Sporobolomyces, in producing 

 two, three, or possibly four or more spores on the end of one and the 

 same sterigma, provides us with a phenomenon which does not find 

 a parallel in any of the typical Basidiomycetes. 



The Successive Production of Spores on Two or More Sterig- 

 mata. — While the production of a single sterigma only seems to be 

 the rule for healthy Sporobolomyces yeast cells growing on a fresh 

 culture medium, yeast cells growing on a more or less exhausted 

 medium often develop two sterigmata and sometimes more. 



1 A. J. Kluyver and C. B. van Niel, loc. cit., p. 18. 



2 These Researches, Vol. II, 1922, pp. 271-273, 355. 



