Growth regulation 



12 



In preceding chapters the principal concepts of plant metabolism, 

 seed germination, and plant nutrition were introduced. In each 

 instance growth was the ultimate result of the various physical and 

 chemical processes described. As pointed out in Chapter 1, growth 

 of a living organism results from a synthetic development from within. 

 Such growth, which implies both enlargement and differentiation, is 

 not haphazard but rather is controlled by several "built-in" series of 

 interrelated factors. In plants, two such series include the genetic or 

 hereditary factors and hormonal or growth-correlating factors, the 

 latter probably being largely dependent on the former. A third group 

 includes the vast number of environmental factors which contribute 

 greatly to the growth of the plant in question. While it is beyond 

 the scope of this book to treat the genetic factors, it is appropriate 

 to discuss the last two groups in some detail. 



ENVIRONMENTAL FACTORS INFLUENCING GROWTH 



Environmental factors influencing the growth of plants can be 

 grouped into three classes, climatic, edaphic, and biotic. Climatic 

 factors influence the growth of a plant through the atmosphere and 

 include such things as temperature, light, carbon dioxide concentra- 

 tion, precipitation and humidity, and wind movement. Edaphic 

 factors operate through the soil and include soil moisture, tempera- 

 ture, aeration, and solute concentration. Biotic factors arise from 

 the presence of other plants and animals. In this group are included 



276 



