64 



PHYSIOLOGY. 



regularly of diminishing density, and that this gives the appearance of alter- 

 nating lines. The starch formed by plants is one of the organic substances 

 which are manufactured by plants, and it is the basis for the formation of 

 other organic substances in the plant, ^^'ithout carbon food green plants 

 cannot make any appreciable increase of plant substance, though a consider- 

 able increase in size of the plant may take place. 



Note. — The organic compounds resulting from carbon conversion, since 

 they are formed by the union of carbon, hydrogen, and oxygen in such a way 

 that the hydrogen and oxygen are usually present in the same proportion as in 

 water, are called carbohydi'ates. The most common carbohydrates are sugars 

 (cane Fugar, C12H22O11, for example, in beet roots, sugar cane, etc.), starch, 

 and cellulose. They are also classed among the non -nitrogenous substances. 

 Other non -nitrogenous plant substances are the organic acids, like oxalic acid 

 (H2C2O4), malic acid (H2C4H4O6), etc.; the fats and fixed oils, which occur 

 in the seeds and fruits of many plants. Of the nitrogenous substances the 

 proteids have a very complex chemical formula and contain carbon, hydrogen, 

 oxygen, nitrogen, sulphur, etc. (example, ah-iiron, or proteid grains, found in 

 seeds). The proteids are the source of nitrogenous food for the seedling 

 dunng germination. Of the amides, asparagin (C4lInN203) is an example of 

 a nitrogenous substance; and of the alkaloids, nicotin (CioHi^No) from 

 tobacco. 



All living plants contain a large per cent of water. According to Vines 

 "ripe seeds dried in the air contain 12 to 15 per cent of water, herbaceous 

 plants 60 to 80 per cent, and many water-plants and fungi as much as 95 per 

 cent of their weight." When heated to 100° C. the water is driven off. The 

 dry matter remaining is made up partly of organic compounds, examples of 

 which are given above, and inorganic compounds, l^y burning this dry residue 

 the organic substances are mostly changed into volatile products, principally 

 carbonic acid, water, and nitrogen. The inorganic substances as a result 

 of combustion remain as a white or gray powder, the ash. 



The amount of the ash increases with the age of the plant, though the per- 

 centage of ash may vary at different times in the different members of the 

 plant. The following table taken from \'ines will give an idea of the amount 

 and composition of the ash in the dry solid of a few plants. 



CONTENT OF 1000 PARTS OF DRY SOLID MATTER. 



Clover, in blossom 



Wheat, grain 



Wheat, straw 



Potato tubers. 



Apples 



Peas (the seed) 



7.44 

 2.36 



33 

 ■77 

 .26 

 •■7 



0.72 

 0,26 

 0-33 

 0.45 

 0.20 

 o. 16 



