4 1 
in the Root- Apex of Phaseolus . 
haematoxylin gave the best results. Other stains, however, were used for 
special purposes. Very careful staining and washing-out is necessary in order 
to exhibit the finer details of nuclear structure, and a good illumination with 
high powers is required for the microscopic examination of the preparations. 
The apochromatic object-glass of Zeiss (2 mm. N. A. 1-40) and an oil im- 
mersion condenser, or Powell and Lealand’s dry apochromatic condenser 
(N. A. -98) were almost always employed ; but a Leitz ^ oil immersion 
lens was also found valuable. Daylight was often used for general work, 
but the light from an incandescent mantle passed through a bull’s-eye con- 
denser was used to determine the finer details of structure. 
I am much indebted to my friend Mr. Norman Walker, Assistant- 
Lecturer in the Yorkshire College, who was kind enough to make some of 
the preparations for me. 
The Resting Nucleus. 
The resting nucleus does not appear to differ materially in structure 
from the ordinary nuclei of plant-cells. It is limited towards the cytoplasm 
by a thin deeply stained layer — the nuclear membrane — which exhibits in 
thin sections a fine granular structure. Inside this is a finely meshed 
nuclear network, which forms a thin layer at the periphery of the nucleus 
in close contact with the nuclear membrane. On it are distributed a num- 
ber of small granules, which stain deeply in nuclear stains. 
Each nucleus contains one or more nucleoli, which are usually much 
more conspicuous than the nuclear reticulum, and stain more deeply. The 
number present varies according to the age of the cell. It is only in the 
young cells, however, that two or more occur ; as the cells come to maturity 
the nucleoli fuse together so that in all the older cells one nucleolus only is 
present. Each nucleolus is lodged in a cavity in the nuclear network, 
and is surrounded by a clear space. As in many other vegetable nuclei, it 
is suspended in this cavity by a number of delicate threads, radiating from 
it on all sides to the nuclear network (PI. V, Figs. 3-7). These threads are 
only visible in stained specimens. They appear to be continuous with 
the nuclear network, and to form a part of it. 
The relative size of the nucleolus and amount of nuclear network varies 
in different cells. In the actively growing and dividing cells of the meriste- 
matic region the nucleolus is the most prominent feature in the nucleus, the 
nuclear network forming only a very thin layer in close contact with, and 
scarcely distinguishable from, the nuclear membrane. In the cells of the 
root-cap the nucleolus is much smaller, but the nuclear network is relatively 
more abundant, and in the outermost older cells of the root-cap layer is in 
its turn the most prominent feature in the nucleus, the nucleoli being so 
small in some cases as to be scarcely visible. The same differences are 
