42 Wager. — The Nucleolus and Nuclear Division 
observable in other parts of the young root. It thus appears that the 
amount of nucleolar substance present in a nucleus is to some extent 
a measure of the nuclear activities. 
Structure of the Nucleolus. 
The nucleolus is spherical in shape or nearly so, and is usually placed 
in or near the centre of the nucleus. It does not lie free in the nucleus, 
but, as already pointed out, is in close connexion with the nuclear network, 
in which it is suspended by fibres which not merely surround it, as Mont- 
gomery states (loc. cit., p. 506), but actually penetrate its substance, and 
in many cases appear as if drawn out of it. The nucleolus in fact appears 
to form a part of the nuclear network. I have observed similar connecting 
fibres in the embryo-sac nuclei of Lilinm in Miss Sargant’s preparations, 
both in nuclei in the resting stage and in synapsis and later stages, in the 
apical cells of the stem of Elodea , in the root-cells of the Oak, and in many 
other cases. They have been observed by Farmer in the nuclei of Liver- 
worts and Lilium ; by Duggar (loc. cit.) in various plants ; by Rosenberg 
in the nuclei of the suspensor of Zostera marina , L., and by other observers 
in various nuclei — both of animal and plant cells. Zimmermann’s statement 1 
that the nucleolus in no case appears to be in direct connexion with the 
chromatin-network is therefore not correct. 
In some cases the nucleolus appears to be homogeneous throughout, 
but in the majority of nuclei it possesses one or more vacuolar spaces filled 
with a substance which appears to differ from the rest of the nucleolus 
(Figs. 1-7, 37). This vacuolization always appears to take place as the 
nucleus comes to maturity. It is absent only in young nucleoli. I have 
not seen the alveolar structure described by Cavara (loc. cit.), but it is 
obvious that the presence of a large number of vacuoles in a nucleolus 
would produce some such appearance as he describes. 
In some of the larger nucleoli I have observed darker coloured granules 
(nucleolini) as described by Macfarlane (loc. cit.) and others, but I agree 
with Montgomery (loc. cit.) that no particular morphological significance 
can be attached to them at present. In the cases observed by me they 
seemed to form only the central portion of the vacuolar substance. 
The vacuolate structure of nucleoli appears to be very common, and 
was first of all noticed in vegetable-cells by Schleiden, who speaks of the 
nucleolus as ‘ a small, sharply defined body, which, judging from the shadow 
that it casts, appears to represent a thick ring or hollow globule V 
Nageli also observes that nucleoli may be homogeneous or ‘ hollow in 
1 Die Morphologie und Physiologic des pflanzlichen Zellkernes. Jena, 1896, p. 40. 
2 Contributions to Phytogenesis. Translated by Henry Smith in 1847 for the Sydenham 
Society, p. 234. See also Schleiden’s Principles of Botany, Eng. Ed., translated by E. Lankester, 
1849, P- 32 . 
