IX. COMPOSITION OF THE BODY 1 



219. Substances Found in Plants. The principal components of 

 living matter are carbon, hydrogen, oxygen and nitrogen, while a 

 few other elements play more or less minor parts in the plasmatic 

 structures. The compounds found on analysis of the body of 

 a plant comprise both the components of the living matter, and 

 also the substances which have been formed by it and deposited in 

 the form of secretions retained in the body, in the cells, or in the 

 form of dead tissues, which serve mechanical uses only. These 

 compounds are proteids, amides, alkaloids, carbohydrates, organic 

 acids, glucosides, fats and fixed oils, and essential or volatile oils, 

 etc., but this enumeration does not give a defined basis from which 

 the study of the metabolism of the plant may proceed until a differ- 

 entiation is made between the substances participating further in 

 the activities of living matter, and those in which no further change 

 is possible. The former which may be known as plastic substances 

 include starch, sugar, inulin, glycogen, cellulose, globulin, amides, 

 fats, oils, glucosides, organic acids, and many others, while the 

 latter or aplastic substances comprise the cellulose of the walls of 

 dead tissues, insoluble crystals of mineral salts, waxy substances, 

 etc. It is to be noted that many substances participate in the 

 construction of both kinds of material. Thus cellulose is in most 

 instances an aplastic substance, but when deposited as reserve food 

 in the seeds of Liliaceae and other plants, it is plastic. 



The outlines of analysis on the following pages will give methods 

 for the detection and estimation of the more important substances 

 which may be extracted from plants. 2 



1 The draft of this chapter was prepared by Mr. J. E. Kirkwood, and Dr. W. J. 

 Gies, who also read proof of the pages. 



2 For the identification of these substances in the tissues, the methods of micro- 

 chemical analysis given in Zimmermann's Botanical Microtechnique will be necessary. 



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