CHAPTKR II. — SPECIAL PHYSIOLOGY OF THE NUTRITIVE FUNCTIONS. 727 



5. The Products of Metabolism. Tlie relation between the 

 anabolism and the eatabolism of the plant may be generally stated 

 thus, that the construction of organic substance in the former is 

 greater than the decomposition of it in the latter, so that on the 

 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 

 plastic p'odiicts, in the latter ivaste-products, of metabolism (see p. 

 670.) 



The most important of the plastic products are enumerated be- 

 low. They are all found accumulated as reserve materials in 

 various parts of plants, though some of them (e.g. amides, glucose, 

 maltose) are more especially the forms in which organic substance 

 is distributed throughout the plant. 



Non-nitrogenous reserve materials : — 



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 tbe 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.). 

 Nitrogemms reserve materials : — 



a. Proteids; in solid granules (aleuron ; p. 112), in seeds, more espe- 



cially oily seeds ; or in the cytoplasm {e.g. latex). 



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



bulbous roots, etc. 



With regard to the mode of formation of these substances, 

 some of them are certainly produced both synthetically and ana- 

 lytically, that is, both in anabolism and in eatabolism, whereas 

 others are only produced in one or other of these ways. 



Fats and Carbohydrates. There is some evidence that fats are formed in the 

 eatabolism of protoplasm : that is, that in the decomposition of the proto- 

 plasmic molecule, fat is frequently one of the products : there is also reason to 

 believe that the purely reserve carbohydrates, starch, cane-sugar, and cellulose, 

 have a similar origin. The other sugars (glucose, maltose) may be formed 

 auabolically, but are also formed by enzymes from the reserve carbohydrates. 



