=169.= The carbohydrates are classed among the non-nitrogenous substances. Other non-nitrogenous plant substances are the organic acids like oxalic acid (H₂C₂O₄), malic acid (H₂C₄H₄O₅), 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_ (C₄H₈N₂O₃) is an example of a nitrogenous substance; and of the alkaloids, nicotin (C₁₀H₁₄N₂) 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. By 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 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 OF 1000 PARTS OF DRY SOLID MATTER. |Clover, in|Wheat,|Wheat,|Potato|Apples| Peas | blossom |grain |straw |tubers| |(the seed) ------------------+----------+------+------+------+------+---------- Ash. | 68.3 | 19.7 | 53.7 | 37.7 | 14.4 | 27.3 Potash. | 21.96 | 6.14 | 7.33 | 22.76| 5.14| 11.41 Soda. | 1.39 | 0.44 | 0.74 | 0.99| 3.76| 0.26 Lime. | 24.06 | 0.66 | 3.09 | 0.97| 0.59| 1.36 Magnesium. | 7.44 | 2.36 | 1.33 | 1.77| 1.26| 2.17 Ferric Oxide. | 0.72 | 0.26 | 0.33 | 0.45| 0.2 | 0.16 Phosphoric Acid. | 6.74 | 9.26 | 2.58 | 6.53| 1.96| 9.95 Sulphuric Acid. | 2.06 | 0.07 | 1.32 | 2.45| 0.88| 0.95 Silica. | 1.62 | 0.42 |36.25 | 0.8 | 0.62| 0.24 Chlorine. | 2.66 | 0.04 | 0.9 | 1.17| ....| 0.42 ------------------+----------+------+------+------+------+---------- FOOTNOTES: [9] Paragraphs 156-160 were prepared by Dr. E. J. Durand.