CHAPTER VIII 

 ORGANIC SUBSTANCES AS PLANT FOOD 



65. Storage of Substances in Seeds and Other Organs. 

 Their Utilization in Germination. Major Groups of Reserve 

 Substances. — The process of nutrition of the plant may be 

 divided into two stages. The first stage consists of the acquisition 

 from the surrounding environment, the soil and the atmosphere, 

 of the necessary raw materials, such as carbon dioxide, water, 

 nitrogenous compounds and the various ash constituents, and the 

 formation from these substances of the food products proper, 

 mainly carbohydrates, fats, and proteins. This stage represents a 

 specific characteristic of the plant organism. A synthetic activity 

 of this nature, effected largely through the chloroplasts, is not 

 available to the animal organism. 



The second stage consists of nutrition in the narrow sensa of the 

 word, or the transformation of the synthesized products into 

 substances from which the cells and tissues are formed. In the 

 first place, this consists in the building of new masses of living 

 protoplasm, and the construction of the secondary structures of 

 the cell, its wall and various kinds of inclusions, etc. In the 

 process of nutrition, the products manufactured by the leaf are 

 subject to complete transformation. A considerable part of them 

 disappear from the organism, being consumed in respiration and 

 serving as material for the acquisition of the necessary energy. 

 This phase of the nutrition of plants does not differ essentially from 

 the nutrition of animal organisms. The fundamental difference 

 between the nutrition of animals and plants is that plants consume 

 substances made by their own synthesis, while animals feed on 

 products formed by plants. 



The first stage in the nutrition of plants has been discussed in 

 the first part of the book. The most convenient way to study the 

 second stage is by starting with the nutrition of the seed just coming 

 to active life. Seeds, in the first place, contain comparatively large 

 and conveniently observable reserves of nutritive substances and, 

 secondly, the utilization of food products proceeds in them at a 



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