214 COLLEGE BOTANY 



Growth. — This is a process which we very va^ely describe 

 as the enlargement of the living organism. We now realize that 

 it is a very complicated process and involves many activities, 

 some of which are chemical and others of which may be purely 

 physical. Growth involves practically all the very complex 

 processes which we have studied and many others. Further- 

 more, it is influenced hy many, external or environmental factors. 

 The evidences of plant growth are the increase in size and 

 weight, the formation of cells, tissues and organs, and repro- 

 duction. A more thorough study shows cell enlargement and 

 division, formation of cell walls, differentiation of tissues and 

 secondary thickenings. 



We see evidences of growth in the germination of seeds, in 

 the elongation of roots and shoots, in the enlargements of leaves, 

 in the formation of flowers and fruits, and in the thickening of 

 many parts. We now know that this growth involves the taking 

 in of water, carbon dioxide, nitrogen and minerals, the absorp- 

 tion of energy from the sun, the manufacture of true foods, the 

 transportation of foods, and the utilization of foods in the forma- 

 tion of new cells. We have also learned that some growths, such 

 as the development of the embryo and cell modifications, are 

 very obscure ; and we have also learned that a plant may increase 

 in size and not increase in dry weight. Although our previous 

 work has involved a continuous consideration of growth, there 

 are some few points that should be given special consideration 

 at this time. 



Storage of Foods and Growth. — The stored foods in the 

 plant sei-ve primarily for the gi'owth of the plant at some later 

 period. This is well illustrated in the case of the seeds, the 

 stored food serving for the support of the seedling until its roots 



