80 



PHYSIO LOG y. 



powder, much smaller in bulk than the charcoal in the former experiment. 

 This is the ash of the plant. 



168. What has become of the carbon ? In this experiment the air was 

 not excluded from the plant material, so that oxygen combined with carbon 

 as the water was freed, and formed carbon dioxide, passing off into the air 

 in this form. This it will be remembered is the form in which the plant 

 took the carbon-food in through the leaves. Here the carbon dioxide met 

 the water coming from the soil, and the two united to form, ultimately, 

 starch, cellulose, and other compounds of carbon; while with the addition 

 of nitrogen, sulphur, etc., coming also from the soil, still other plant sub- 

 stances were formed. 



169. The carbohydrates are classed among the non-nitrogenous sub- 

 stances. Other non-nitrogenous plant substances are the organic acids 

 like oxalic acid (H 2 C 2 O 4 ), malic acid (H 2 C 4 H 4 O 5 ), 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, aleuron, or 

 proteid grains, found in seeds). The proteids are the source of nitrogenous 

 food for the seedling during germination. Of the amides, asparagin 

 (C 4 H 8 N 3 O 3 ) is an example of a nitrogenous substance; and of the alkaloids, 

 nicotin (C ;0 H 14 N 2 ) 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, exam- 

 ples of which are given above, and inorganic compounds. By burning this 

 dry residue the organic substances are mostly changed into volatile prod- 

 ucts, principally carbonic acid, water, and nitrogen. The inorganic sub- 

 stances 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 

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

 the plant. The following table taken from Vines will give an idea of the 

 amount and composition of the ash in the dry solid of a few plants: 

 CONTENT OP 1000 PARTS OF DRY SOLID MATTER. 



