Chaptee VIII 

 HOW THE PLANT LIVES 



B. M. DVGGAR 



1. The Plant Activities 



182. The plant is a very dependent struc- 

 ture: it must be supplied with water and certain 

 soluble salts from the soil, oxygen and carbon 

 dioxid from the air, in addition to sunlight and 

 a certain amount of heat. When these con- 

 ditions are fulfilled, — somewhat as a plant's 

 ancestors have been accustomed to them. — 

 the plant must grow, provided no extraneous 

 diseases or accidents overtake it. 



183. A growing plant is influenced by all 

 of the external conditions about it, — it is sen- 

 sitive, or manifests irritability. In studying 

 growth processes, we must remember that these 

 processes are occurring in a highly responsive 

 living object, an object with both inexplainable 

 internal forces and with processes most favor- 

 able for chemical and physical study. To study 

 how a plant lives, one must consider the im- 

 portant factors of growth, actual growth phe- 



(112) 



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