13 
THE YEAST-FUNGI IN NATURE.* 
F. A. MASON, F.R.M.S", 
Leeds. 
THE terms Yeasts and Yeast-Fungi used in the following notes 
refer to those minute, mono-cellular, spore-forming organisms, 
belonging to a family bearing the significant title Saccharomy- 
cete@. It is desirable to make this explanation because there 
also exists a large number of mono-cellular plants which so 
much resemble the true yeasts as to make it almost impossible 
to distinguish, by ordinary microscopical examination, the 
one group from the other; these include such organisms as 
Torula, Mycoderma, Oidium, etc., which may be descrbied 
as Yeast-like Fungi, and the only difference which need be 
remarked here, is that they do not under any known circum- 
stance produce spores. 
The common belief that Yeasts may be found only in a 
brewery or associated with commercial products of fermentation 
has no foundation in fact. These organisms are as widely 
distributed in nature as any of the fungi, and whereas some 
80 species have been identified, only one is cultivated for brewing 
purposes, at any rate so far as British practice 1s concerned. 
Unfortunately, other species do sometines find their way into a 
brewhouse, but every advantage that science can teach is 
exercised in endeavouring to check their entry or to combat 
their development should it be effected. 
In company with their relatives, the moulds, and their 
more distant friends, the bacteria, yeasts may be found every- 
where if proper precautions are taken to secure them. An 
exposed Petri dish containing nutrient gelatine, preferably 
prepared with malt-wort, will reveal their presence in the 
atmosphere. Here they may be detected all the year round, 
but Spring and Autumn are the seasons in which they are 
especially abundant ; a fact of great interest in its relation to 
the varied life-history of these minute organisms. 
Most commonly do they occur upon the surface of ripe and 
ripening fruit. Apples, pears, plums, strawberries and 
especially grapes are the chief breeding places ; some species 
on one, some on another, often several species side by side on 
the same fruit. All the yeast cell requires in the way of nutri- 
ment is amply provided by the sweet juices of the fruits, and 
in these situations the yeasts develop by the apparently simple 
reproductive process of budding. Under the most favourable 
conditions with regard to moisture, temperature and food 
supply, reproduction can proceed with almost inconceivable 
rapidity, but fortunately perhaps, this ideal state of existence 
does not much prevail in nature. 
* Read at the meeting of the Yorkshire Mycological Committee, 1912. 
1913 Jan. 1. 
