CHAPTER XIII 



GROWTH 



A PROPER conception of growth and important growth 

 relations is fundamental in plant production. Growth 

 necessarily receives consideration at least indirectly 

 throughout every chapter, for it enters into any discussion 

 of the relation of the plant to factors of environment ; to 

 the making, use, and accumulation of food-materials ; 

 and to the phenomenon of reproduction as well. In gen- 

 eral, the practical measure of growth is yield. It is im- 

 portant, however, to examine somewhat more carefully 

 certain observations and fundamental facts regarding the 

 mechanism of growth. 



175. The factors. - - Growth is conditioned by internal 

 and external factors. Among the internal factors must 

 be assumed vitality, not explainable, yet known as an 

 attribute of the living mechanism ; heredity, operating to 

 reproduce specific form ; and often a certain food-supply. 

 The external factors are many of the environmental con- 

 ditions previously enumerated (section 5) ; and essential 

 are moisture, a certain range of temperature, a source of 

 oxygen, the several nutrients and crude food-materials, 

 and (for continued growth in green plants) light. These 

 factors in relation to growth and development receive 

 special consideration as independent topics. 

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