THE STRUCTURAL COMPONENTS OF PROTOPLASTS 13 



protein only, or both amorphous antl crvstalhno components; other 

 substances may be present also. Protein res(n'V(\s are w<'ll known in the 

 yolk of animal eggs where they commonl.\- occur in associnlion with l';itty 

 yolk globules. 



Plants infected with some viruses show characteristic intracellular 

 bodies not present in normal tissues. These are amorjjhous in some 

 cases, while certain other viruses result in the formation of l)otii am(n-- 

 phous and crystalline inclusions. Insoluble complexes reseml)ling the.se 

 can be produced artificially by combining purified viruses with proteins 

 of certain kinds, which suggests that such bodies in infected tissues may 

 be similar combinations of the virus with normal or abnormal materials 

 of the host plant. This single example may serve as a remindei- of the 

 mutual assistance rendered by cytology and pathology. 



Fats and oils occur as reserves in the form of globules in the cj'to- 

 plasm of many plant and animal cells, particularly in seeds, spores, and 

 eggs. Minute lipide globules are of common occurrence in the cytoplasm 

 of active cells. Ver}^ large oil globules are sometimes encountered (Fig. 

 33). Waxes are ergastic products of importance in many plants. 



Inorganic crj^stals form another class of ergastic substances (Fig. 34). 

 These occur in great variety in plant tissues, the needle-shaped "raph- 

 ides" composed of calcium oxalate being very frequently encountered 

 in cytological work on living tissues. 



Ergastic substances, then, are of man}- kinds. The same chemical 

 compound maj^ occur at any one moment as a relatively inert mass in 

 the protoplast; at another moment it may be in solution and participat- 

 ing actively in the work of the protoplasm. Ergastic matter is therefore 

 to be characterized by its relative inactivit,y rather than its composition. 

 This is in harmony with the view adopted in the follo^^^ng chapter, viz., 

 that protoplasm is an organized living system of substances that by 

 themselves are not li\ing. 



