102 



present experiment, we may be reasonably v-ure that the zero 

 point of all the integrating instruments 's the SToe. At the 

 end of the growing period however, the "setting" of th^ instru- 

 ment is not known, since we do not know what cycle of changes 

 the internal conditions of the plant have gone through. In 

 order to apply the data secured from standard plants to plant 

 growth in general, it woiJd seem necessary to correct the 

 recdings of the s ' andard plant in the same way that the readings 

 of any physical instrument are corrected for instrumental varia- 

 tions. At present no way is known by which a number can be given 

 to the reacting ability of a plant or to the stages of the cycle 

 through which the plant passes as it matures. Variations in 

 the internal conditions of the plant such as these here noted 

 must be responsible for the fact that the seasonal avera es of 

 the two-week leaf-product value, a plant measurement propor- 

 tional to the leaf area and dry weight of the two-week plants, 

 registers a given set of climatic conditions different from the 

 way in which this set is registered by actual leaf area and 

 dry weight of 'he same r^lants grown for four-weeks. 



Several methods suggest themselves by means of which the 

 difficultji noted above may be surmounted. One possibility is 

 to evaluate the internal conditions of the plant and correct 

 the readings for changes in those conditions. This method 

 would involve a detailed study of the standard plant and at best 

 would seem to promise a solution of the problem involving com- 

 plicated mathematical reiuctions of the plant readings. There 

 is every reason to believe th .t a correction formula for plants 

 considered as integrating instruments would, if obtainable, be 

 exceedingly complex. Another, and apparently more honeful 



