45] CHAP. II. PHYSIOLOGY OF NUTRITIVE FUNCTIONS. 201 



whole there is an accumulation of organic substance in the body of 

 the plant. The organic substance is accumulated to some extent 

 in the actual structure or fabric of the plant, as protoplasm and 

 cell-wall, and to some extent in the form of "compounds which 

 may be present in some or all of the cells, but which do not 

 constitute any portion of the fabric. These compounds may or 

 may not be of nutritive value ; in the former case they are termed 

 jrtasfic products, in the latter icaste-products, of metabolism (see 

 p. 158). 



The most important of the plastic products are enumerated be- 

 low. They are all found accumulated as reserve materials iu 

 various parts of plants. 



Non-nitrogenous reserve mattriaJs: 



a. Carbohydrates; in solid granules, starch; in many seeds, and 



tubers, 



in thickened cell-walls, cellulose ; as in Date- 

 seed, Coffee-seed, Vegetable Ivory, 



dissolved in cell-sap ; grape-sugar, as in the Onion 

 and in fruits ; cane-sugar, as in the Sugar-cane 

 and the Beetroot ; inulin, as in the Jerusalem 

 Artichoke and Dahlia. 



b. Fats ; in drops in many seeds (Rape, Linseed, Castor-oil, Palm. 

 etc.). 



Nitrogenous reserve materials : 



a. Proteids ; in solid granules (aleuron ; p. 80), in seeds, more espe- 

 cially oily seeds. 



6. Amides; asparagin, etc., in solution in the cell-sap of bulbs, 

 tubers, bulbous roots, etc. 



The icaste-products are most probably all formed as the result 

 of catabolic processes ; though their formation is often associated, 

 both as to time and place, with active anabolism. They may be 

 classified into nitrogenous and non-nitrogenous. 



The principal nitrogenous waste-products appear to be the 

 alkaloids (see p. 186). They are probably products of the nitro- 

 genous catabolism of plants ; and it is suggestive that they prin- 

 cipally occur deposited in "the cells of deciduous parts, such as 

 leaves, seeds, bark, etc. 



The principal non-nitrogenous waste-products are, water; free 

 oxygen (green plants in light) ; carbon dioxide, and some other 

 highly oxidised carbon-acids, such as the oxalic ; resins and ethereal 

 oils, tannins, aromatic substances, etc. 



Of these waste-products, some are retained in the cells of the 



