CHIEF ENVIRONMENTAL CONDITIONS. 131 



3. THE DURATION ASPECT OF THE TEMPERATURE RELATION. 



The velocities of the many physical and chemical changes that 

 compose vital activity as a whole, depend, as has been seen, upon the 

 temperature. It follows that the outcome of each separate process, 

 and that of the entire complex, is largely determined by the degree of 

 temperature and by the length of the time period during which any 

 temperature has obtained. The accomplishment of the entire plant, 

 as measured by the amount of its growth, for example, might be the 

 sunmiation of the various accomplishments of the component processes 

 during the given time period, which latter are simply the integrations 

 of the various process velocities with respect to time. Since we are 

 very far from being able satisfactorily to separate the component 

 processes that go to make up the activity of any plant, it is necessary 

 here only to call attention to the above proposition as representing a 

 general principle the details of which must occupy many minds in 

 the future. For the present the physiological ecologist can do nothing 

 but consider the varying velocities of certain broad, complex processes 

 such as growth, crop production, and the like. But our generaliza- 

 tion is of use at least in this, that it enables us to lay out the field 

 for future study, with a probability of satisfactory results that might 

 otherwise be absent. 



We have seen that physical and chemical processes are intimately 

 commingled in the intricate complex which we call life. To this con- 

 ception may be appended the additional one that many of the physical 

 properties, probably all of them in the final reckoning, depend upon 

 chemical changes which have previously occurred. It is quite im- 

 possible for a physical change to occur in the substance of a plant 

 unless the various materials involved be present, and these may be 

 assumed, in general, to have resulted from chemical changes. Since 

 we know already that chemical action is exceedingly important in most 

 plant phenomena, the last statement allows us tentatively to state 

 that this action may probably be found to have the controlling in- 

 fluence in general life activities.^ If this be true, the general activi- 

 ties of the plant should follow more or less accurately the principles of 

 chemical action. The relation of chemical processes to temperature 

 have been much worked upon and the Law of Van't Hoff and Arrhenius 

 has been developed in this connection. It states that for each rise 

 in temperature over a range amounting to 10 centigrade degrees, there 

 is a doubling or tripling of the reaction velocity. Often the coefficient 

 is 2 or a little more or less (PH3 = P+H3, 1.2; C2H3O2 . CoHs+NaOH, 

 1.89)2. Usually it is between 2 and 3 (CsHaONHaAg, 2.12; C2H3CIO2. 



1 The whole matter here brought forward has been given somewhat more thorough considera- 

 tion than is needed here, in the following paper: Livingston, B. E., and G. J. Livingston, Tem- 

 perature Coefficients in Plant Geography and Climatology, Bot. Gaz., 56: 349-375, 1913. 



* Van't HofT, J. H., Lectures on theoretical and physical chemistry, translated by R. A. 

 Lehfeldt. London, no date (author's preface date 1898), part 1, p. 228. 



