1 54 CHEMICAL COMPOSITION OF PLANTS 



The amount of water in ripe seeds is comparatively small, 

 generally averaging from 10 to 15 per cent. In succulent fruits, 

 fleshy roots, tubers, green leaves and fresh vegetative organs, it 

 is rarely less than 75 per cent, and not unfrequently as high as 

 85 to 90 per cent, of their total weight. 



The proportion of ash in the dry matter of seeds and succulent 

 roots and tubers is generally very much smaller than in the 

 leaves and bark of plants. 



Ex. 78. — Weigh pieces of carrot, turnip, mangel, potato, apple and 

 strawberry in separate porcelain dishes, then cut each piece into several small 

 pieces and place the porcelain dishes and contents in a warm oven or ' water- 

 oven.' Weigh at intervals of three hours and note the loss in weight. 



Ex. 79. — Repeat the previous experiment with leaves of potato, turnip, 

 ash and other trees, freshly-cut grass, and freshly-ground ' whole-meal ' 

 flour, oat-meal and bean-meal. 



3. The dry matter of a plant consists of (i) a small amount of 

 unutilised inorganic substances absorbed from the soil; and (2) 

 a large amount of various organic compounds manufactured by 

 the plant out of the food-materials which it has absorbed from 

 the soil and air. 



To merely give a list of the compounds met with in plants 

 would fill a large volume : it is, however, not needful here to 

 describe more than the chief organic substances of which the 

 plant-body is composed : for present purposes they may be 

 classified into two groups, namely : — (i) non-nitrogenous and 

 (2) nitrogenous substances according as they are free from or 

 contain nitrogen. 



