18 BIOLOGY 



when treated with different staining substances. It 

 is now supposed that these granules are the products 

 of the living substance, and useful in its various 

 activities. Which of these granules actually belong 

 to the cytoplasm it is difficult to say, as we un- 

 doubtedly find many granules in certain cells, which 

 may be looked upon as reserve foodstuff, and in others 

 substances are found which are the products simply of 

 the cellular activity, and are present at one time, absent 

 at another. 



In such cells as the protozoan amoeba, paramcecium, 

 and others, granules exist temporarily which may be 

 the unutilised products of digestion. 



In the plant cells it is even more difficult to say which 

 of the granules are essential and which are not. Certain 

 granules in plants are without doubt not essential part 

 of the cytoplasm at all, for example, the starch and 

 aleurone grains, and numerous crystal-like bodies such 

 as oxalates. 



The second essential structure of the cell is the 

 nucleus. It appears usually as a spheroidal mass in its 

 more perfect form, the size of which bears a definite 

 relation to the size of the cell. It is usually enclosed 

 by a definite membrane-like outer coating, and consists 

 of a fluid-like substance and also of a material that is 

 more or less filamentous in appearance. By the use of 

 various stains we are able to recognise that the nuclear 

 substance is different from the cytoplasm chemically, 

 and our knowledge of cell- structure has been largely 

 increased by a study of the effects of the different 

 staining reagents on the various parts of the cell. 



Of the various substances found in a cell, the chief 



