Wager. — -The Nucleus of the Yeast- Plant. 527 
The single nuclear vacuole of the Yeast-cell thus has its 
origin in many cases from a fusion of numerous small 
vacuoles, and these smaller vacuoles are developed in all 
probability from the granules in the protoplasm. 
There are some small cells however which contain only 
one vacuole. This, as we shall see later, probably arises by 
a division of the parent vacuole in the mother-cell. 
Glycogen-Vacuoles. 
Errera (’82, ’85, ’98), Clautriau (’95), and others have 
shown that the Yeast-cell contains glycogen. It is not equally 
abundant in all stages of growth. In the earlier stages of 
fermentation it is more abundant than in the later stages. 
As fermentation proceeds the glycogen is used up, and finally 
in old cultures practically no glycogen is to be seen, a few 
cells here and there only exhibiting the characteristic reaction 
when treated with iodine. 
In the majority of cases the glycogen is located in a large 
vacuole in each cell which appears shortly after fermentation 
has commenced ; but during the first two or three hours the 
glycogen when present is mainly diffused through the proto- 
plasm. In the glycogen-containing cells when stained with 
iodine, the nucleus is generally visible as a transparent, colour- 
less or slightly greenish refractive body, sometimes spherical, 
sometimes flattened against the cell-wall (Figs. 23 - 25 ). Some- 
times the entire cell-contents, with the exception of a thin 
lining-layer of protoplasm on the cell-wall, consist of this 
substance, which according to Errera (’85) doubtless plays the 
same part as starch in the higher plants. 
So far as can be observed at present, the glycogen is located 
in a special glycogen-vacuole. It never appears, or only to 
a slight extent, in the nuclear vacuole. If a cell containing 
glycogen be stained for a few seconds in acetic methyl-green, 
the nuclear body and lining-layer of protoplasm become 
stained. If now a solution of iodine be added and the cells 
mounted in dilute glycerine, a beautiful double colouration 
