CHAPTER VIII 

 GROWTH 



We have learned that food provides the plant with the energy 

 needed to carry on its various functions. A large part of the 

 food which the plant manufactures is therefore either broken 

 down directly by respiration, to liberate energy for immediate 

 use, or is stored up to meet requirements of this sort which may 

 later arise. A healthy plant, however, produces more food than 

 is necessary to maintain the activities of its living substance, 

 and the surplus may be built into the tissues and used to pro- 

 duce new protoplasm and new cell walls, thus promoting the 

 growth of the plant body. Growth represents the excess of con- 

 structive over destructive metabolism. A knowledge of just what 

 it involves, and of just how it takes place, is evidently necessary 

 if we are to arrive at a clear understanding of the structure and 

 development of the plant body. 



The term "growth", in its simplest usage, refers to any 

 increase in size, either of the whole organism or of its parts. 

 This expansion may be a mere swelling brought about by a vigor- 

 ous absorption of water, or it may be due to an increase in bulk of 

 actual plant material — protoplasm and the dead structures 

 secreted by it. All early stages in growth are of the former 

 type, and the swollen and succulent tissues thus produced 

 gradually attain to normal firmness through the deposition within 

 them of large amounts of new material. Indeed, early growth 

 may be accompanied by an actual, though temporary, decrease 

 in dry weight. 



In studying this process of growth in the plant as a whole we 

 must remember that the plant body is made up of a mass of 

 minute cells. The size of the cells in any particular tissue and 

 within the same species is rather constant, and is believed to 

 approximate the size which is most efficient for that particular 

 tissue. Very large cells and very small cells would evidently 

 possess many disadvantages. It is therefore clear that growth 

 must consist in the production of more cells rather than in the 



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