the Yeast Plant. 
77 
nuclear network in consequence shows up more clearly, but it seems not to 
disappear entirely except during spore formation. 
The strands of the nuclear network occur mainly at the periphery 
of the vacuole, a few delicate threads only being visible in the central 
region of the vacuole. They are thicker and more prominent where they 
join the nucleolus than elsewhere. 
Both nucleolus and network may become more or less impregnated 
with chromatin, and granules of chromatin are found under conditions 
of great fermentative activity on the nuclear network and in a mass around 
the nucleolus and partly embedded in its substance. There it forms a dense 
peripheral layer, which gives the nucleolus its strong capacity for stains 
at certain stages. 
The variation in the amount of the strongly stainable chromatin sub¬ 
stance present both in the nucleolus and the network probably depends 
upon the variation in metabolic activity in the life of the yeast cell. It is 
most abundant at the period of highest fermentative activity. In the early 
stages of fermentative activity, and during the preliminary stages of spore 
formation, the cytoplasm stains very deeply with nuclear stains, and gives 
a reaction for phosphorus and iron. This appears to be due, as Macallum 
first pointed out (’ 95 , ’ 98 , and ’ 99 ), to chromatin diffused through it. It 
soon disappears as fermentation proceeds, and the deeply stainable granular 
chromatin around the nucleolus then becomes more distinctly visible. 
The basis of the nucleolus and nuclear network appears to be 
a homogeneous substance, which does not possess a strong affinity for stains, 
and gives the reaction of the plastin network of the nuclei of higher plants. 
At certain stages the chromatin granules disappear almost entirely 
from both nucleolus and network, with the exception of a single deeply 
stainable patch on one side of the nucleolus. Even when a large quantity 
of chromatin is present, this black patch can be brought into prominence 
by prolonged washing out of the stain. Sometimes the amount of chromatin 
present is so small that the nucleolus appears as a small colourless or nearly 
colourless body with a dark granule (or more than one) on one side of it. 
It is probably this that has given rise to the erroneous interpretation 
of many observers that the nucleolus itself is a nucleus with a nucleolus, 
chromatin granules, and nuclear sap. 
The prominence of the nuclear vacuole at the height of fermentation, 
the appearance of chromatin on the network at its periphery, and the dis¬ 
appearance of the diffuse chromatin from the cytoplasm, suggest that 
possibly the vacuole plays an important part in the elaboration of chro¬ 
matin material which is excreted into the cytoplasm to be used up in the 
metabolism of the cell during its active fermentation. 
The nucleolus and the chromatin network give a distinct reaction for 
phosphorus and iron. The cytoplasm, during the period when it stains 
