Nutrition. 83 



give the amount of the dry matter in the plant, consisting of 

 organic and inorganic compounds. Subtract weight of dry 

 matter from original weight of material, obtaining the amount 

 of water originally present, which has been driven off by heat. 

 This will also include any volatile substances originally present. 

 Now place the crucible in the flame of a Bunsen burner, where 

 it will incinerate. The process should be continued until the 

 ash is nearly pure white. Some precaution must be taken that 

 particles of the substance are not carried away by currents of 

 air rising above the flame. Obtain the weight of the ash com- 

 prising the mineral substances in the plant, and subtract from 

 the weight of the dry matter. The remainder will indicate the 

 amount of organic present material in the leaves. Calculate 

 the percentage of the three groups of constituents. Repeat 

 with stems and fruits. 



It would also be profitable to make an analysis of young and 

 old leaves of some species to note variations in the proportions 

 of the chief constituents. 



The demonstration of starch, sugar, oil, wax, cellulose, pro- 

 teids, acids, nuclein, glucosides, etc., may be accomplished by 

 methods given in detail in text-books on micro-technique. 

 (Directions for an analysis of the plant are outlined in Mac- 

 Dougal's "Practical Plant Physiology," pp. 147-174.) 



80. Food elements of plants, — The elements used by 

 the plant in the preparation of its food are carbon, hydrogen, 

 oxygen, nitrogen, potassium, calcium, phosphorus, sulphur, iron, 

 and magnesium. Carbon is obtained chiefly from the air, 

 oxygen from the air and soil and some carbon, and all of the 

 other elements named are derived from the soil. Oxygen is in 

 the form of compounds in the soil and as a free gas in the air. 

 Carbon is in the form of carbon dioxide in the air and in 

 various compounds in the soil. The other elements occur in 

 combination in the soil, from which they, as all soil constituents, 

 are taken up in watery solutions. 



