CHAPTER IV. 



METABOLISM. 



Quantities of starch formed, and their significance for the 



plant. The absorption of energy the conversion of 



energy in the plant. The plant is a complex machine 



for concentrating and stori?ig energy and material 



from ivithout. 



Sachs measured the increase in dry weight (due 

 to the carbohydrates formed in the chlorophyll- 

 corpuscles) per square meter of leaf-surface, 

 exposed for a definite period, by drying rapidly 

 at ioo"C. equal areas of the leaves concerned, 

 and comparing the weights. 



Of course the results are not to be pushed too 

 far, in view of the fact that some of the starch is 

 continually passing away to be utilised, and of the 

 difficulties of comparing the weather, the intensity 

 of light, currents of air, hygroscopic conditions of 

 atmosphere, and other variable factors which 

 influence the matter. For instance, the stomata 

 open and close to different extents according to 



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