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, ft ft, 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 



