the Yeast Plant. 
57 
particularly in those from the bottom, the network is much reduced, and 
the greater part of the cell is occupied by the large glycogen vacuole 
(Fig. 145)- On the disappearance of the glycogen the chromatin net¬ 
work again expands until it occupies about a third of the cell space 
(Figs. 146, 147). 
The cytoplasm usually stains in inverse proportion to the size and 
staining capacity of the chromatin network, so that when we have a com¬ 
paratively small vacuole, as in the early stages of fermentation, the cyto¬ 
plasm is commonly deeply stained, and when a large conspicuous chromatin 
network is present during the most active period of fermentation, the 
cytoplasm remains almost completely unstained. In cells supplied with 
insufficient nutriment, the vacuole is much reduced in size and is often 
no larger than the nucleolus. As under these conditions the amount 
of stainable material in the nucleus is very small, both nucleolus and 
vacuole appear as faintly stained, pale areas in the cytoplasm, but at the 
periphery of the nucleolus deeply stained granules of chromatin are visible 
( Fi g s - 57 . 5 8 )- 
Generally, it may be stated that in healthy cells a faintly stained 
nucleolus corresponds with a large well-stained chromatin network ; deeply 
stained nucleoli occur when the chromatin network is small, namely, in the 
early stages of fermentation and in cells containing a large amount 
of glycogen (Figs, no, 112); and again, immediately preceding spore 
formation, when the chromatin network has disappeared. 
The prominence of the nuclear vacuole during the active period 
of fermentation suggests that it may play an important part in the meta¬ 
bolism of the cell. At certain stages the chromatin-like substance is 
abundant at the periphery of the vacuole, but at other times the vacuole 
is masked by the cytoplasm, which stains deeply and gives a diffuse re¬ 
action for phosphorus (as Macallum has shown). These facts seem to 
indicate that the chromatin may pass into the cytoplasm, and that the 
nuclear vacuole contains and possibly elaborates chromatin material 
for the use of the cell during its active growth and development. 
The yeast nucleus does not possess a definite nuclear membrane, so that 
the passage of the chromatin from the vacuole into the cytoplasm or vice 
versa is not impeded, as might be the case in the nuclei of higher plants. 
But in these, as is well known, the nuclear membrane disappears at certain 
stages, and it has been suggested that this is to make possible a free inter¬ 
change of nuclear and cytoplasmic material and a renewal of the vital 
activity of the cell. It is possible that in the yeast cell there is a constant 
interchange of stainable material (chromatin) between the nucleus and the 
cytoplasm. 
It is impossible to give any satisfactory account of the elaboration 
of chromatin and its function in the metabolism of the cell. The sequence 
