CHAPTER V. 



NUTRITION. 



78. Composition of the body. The body of a plant is 

 composed of carbon, oxygen, hydrogen, and nitrogen, together 

 with various elements which are united in the form of com- 

 pounds which may be grouped under the proteids, amides, al- 

 kaloids, carbohydrates, organic acids, glucosides, fats, fixed 

 oils, volatile oils, etc. To make a complete analysis of the 

 composition of a plant would require the facilities of a chemical 

 laboratory, and may not be undertaken in connection with this 

 work ; but the presence and localization of various important 

 substances may be demonstrated by the use of simple methods. 



It is important to bear in mind that the body of a plant in- 

 cludes not only the plastic substances, which may be used by 

 the living matter in carrying on various processes, but also large 

 quantities of insoluble aplastic material, which is not capable of 

 being used except in a mechanical way. 



79. Determination of organic and inorganic sub- 

 stances in plants. Secure enough fresh mature leaves to 

 make about 20 to 50 grams, and weigh carefully. Now divide 

 into fine shreds, taking care that none of the material is lost. 

 Place in a small crucible, and set in an oven or over a burner 

 where it will be kept at a temperature slightly above the boil- 

 ing point. Weigh a few hours later, and note amount of loss. 

 Replace over flame, and weigh again after further exposure to 

 heat. Note the weight from which no further decrease may be 

 made. Subtract the weight of the crucible, ascertained before 

 the desiccation was begun, from the total weight. This will 



