36 
Wager. — The Nucleolus a?id Nuclear Division 
This seems to show that the chromatin-nucleolus always stands in 
genetic relation to the chromatin, whilst the nucleolus proper does not. 
The mode of transportation of the nucleolar substance to the daughter- 
nucleoli is probably different in different objects. A discharge of nucleolar 
substance into the cytoplasm appears to take place in some cells and may 
disappear, hence ‘the substance of the parent-nucleolus may be in many 
cases not transferred to the daughter-nuclei, but the latter (perhaps as 
a rule) may produce their own nucleoli de novol There is no substantial 
basis for Zimmermann’s conclusion * omnis nucleolus e nucleolo,’ and 
there is no evidence that the nucleoli are genetically related to the 
chromatin. 
The nucleolus ‘is derived in the first place from the cytoplasm,’ and 
consists ‘ of a substance, or different substances, taken into the nucleus from 
the cell-body.’ ‘ It seems probable that these substances stand in some 
relation to the nutritive processes of the nucleus, and in a relation to the 
growth of the latter. 5 Thus growing nuclei are ‘ characterized by an 
especially large amount of nucleolar substance. 5 From this one might 
conclude that the nucleolar ‘ substance stands in some connexion with the 
processes of nutrition 5 and is either: (i) ‘nutritive in function, 5 or (2) 
‘represents that portion of substances assimilated by the nucleus from 
which all nourishment has been extracted, and in this case it would be 
a waste product, 5 or (3) ‘ may represent accumulations of nutritive substance 
retained in the nucleus as a reserve supply ; but this does not seem to be 
very probable, for by this assumption it would be difficult to explain the 
uniformity in the size of the nucleoli in a given species of cell.’ 
Cavara 1 has made an important contribution to this subject by his 
researches on the nucleoli of various plant-cells. I abstract briefly his 
chief conclusions. Nucleoli in a state of rest in. cells still capable of 
division or growth are composed of two substances, one, internal, which 
forms the major part, a homogeneous and specially refractive substance, 
only slightly stainable, which corresponds to the plastin of Zacharias or 
pyrenin of Schwarz ; the other, peripheral, of variable density, much 
more stainable than the plastin, with characteristics that connect it with 
chromatin or a modification of chromatin. These two substances are 
associated in various ways : sometimes the chromatin-like substance is 
uniformly distributed around the plastin, or more frequently is not so 
uniform, but presents breaks in its continuity which give to the nucleoli 
an alveolate structure or sometimes even a real reticulate structure. 
During the prophases of division the nucleoli decrease somewhat in volume 
and break up. At the same time the linin-thread contracts and breaks 
1 Intorno ad alcune strutture nucleari. Estratto dagli Atti del R. Istituto Botanico dell’ 
Universita di Pavia, nuova serie, v, 1898. Breve contribtizione alia conoscenza del nucleole. 
Bollettino della Societa Botanica Italiana, 1902, p. 108. Bot.Cent., xxxix, 1902. 
