8 VEGETABLE PHYSIOLOGY 
of the space is not filled with protoplasm, the part in 
which the nucleus lies is connected with the lining 
layer by means of strands or bridles. In other cases 
the nucleus is embedded in some part of the lining layer 
itself. This body has a more definite structure than the 
rest of the cytoplasm; it is bounded at the surface by a 
delicate membrane, which is thought, however, to be a 
denser layer of the protoplasm of the cell, rather than to 
belong to the nucleus itself. Within this nuclear membrane 
are found two substances which differ from each other in 
their power of staining with various reagents. The bulk 
of the nucleus is composed of a semi-fluid material known 
as nucleoplasm, in which is embedded a network of fibrils 
or a long much-coiled thread. The fibrils, or the thread, 
are composed of a hyaline substance in which lie, close to 
each other, a number of granules which stain deeply with 
many colouring matters. The threads contain these 
granules in such large proportion that, except with very 
high magnification, the latter cannot be distinguished, and 
consequently the whole fibril appears stained. The fibrils 
are generally said to be composed of chromatin, the name 
having reference to nothing more than this reaction to 
stains. 
One or more small deeply staining bodies, termed 
nucleoli, are found in each nucleus, sometimes being very 
prominent, and at other times hardly distinguishable from 
the nodes of the fibrillar network or the crossings of the 
coiled-up thread (figs. 6, k k, and 9, b). Chemically the 
nucleus resembles the rest of the protoplasm to a consider- 
able extent. It contains, however, a material known as 
nuclein, of which phosphorus is a constituent. It is not 
known how the nuclein is related to the rest of the nuclear 
substance, but it appears to be present in the thread or 
fibrillar network and not in the general nucleoplasm. 
It is of such protoplasts or aggregations of small portions 
of living substance that all plants are built up. There is, 
however, a wonderful variety in the relative arrangements 
