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LECTURES TO SCIENCE TEACHERS. 



3 A.M., the other from 7 A.M. to 10 A.M. We have now to 

 account for these intermissions in the process of growth, 

 and to discover whether they bear any relation to variations 

 occurring in the external circumstances to which the plant 

 was exposed. These external circumstances were (1) a 

 supply of air, (2) a supply of moisture, (3) the action of 

 temperature, (4) the action of light. 



We may fairly assume that of these the first two were 

 invariable during the course of the experiment, and we 

 need not therefore regard them any longer as elements of 

 the problem. It remains for us to consider the action of 

 temperature and of light upon the growth of ^.e plant. 



In discussing the question as to how much changes of 

 temperature have contributed to the production of these 

 tracings, we must recall the general law at which we have 

 already arrived, which indicates the relation existing 

 between temperature and plant life. From this we are 

 able to assert that a slight rise of the atmospheric tempe- 

 rature will stimulate the process of growth, whereas a 

 slight fall will depress it. Now we shall be probably 

 correct in saying that the temperature of the air will 

 gradually sink from 6 P.M. until sunrise (3 A.M.), after 

 which it will gradually rise, until it begins to sink again 

 in the afternoon (4 P.M.). We should therefore expect to 

 lind that the process of growth would be arrested, or at 





