CHAPTER II 



SOME CONDITIONS INFLUENCING GROWTH 

 AND DEVELOPMENT 



It is common knowledge that a certain amount of 

 heat and an adequate supply of air and moisture are 

 essential for plant growth. All plants that have green 

 leaves require light, in addition, to enable them to as- 

 similate carbon dioxid from the air, dissociate it into its 

 component parts, and elaborate the carbon into such 

 complex substances as starch, sugar, and other carbo- 

 hydrates. 



Influence of Light on Yield. — E. Pagnoul' placed 

 colored glass over different potato plants. Two plants 

 under darkened glass elaborated 31 and 20 grams of 

 starch respedlively, while those under ordinary glass 

 elaborated 170 and no grams; at the same time plants 

 under normal conditions elaborated 223 and 361 grams. 

 To the favorable influence of abundant light this writer 

 attributes the large yield of potatoes in a season when 

 the aggregate number of hours of sunshine is unusually 

 large. At Wisconsin Experiment Station coldness and 

 cloudiness were believed to be the causes of a poor 

 yield.' 



The Amount of Moisture. — The amount of 

 water the plant can obtain from the soil is closely cor- 



> E. S. R., v., p.116. a Wis. Report, 1902, p. 188. 

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