258 LIVINGSTON— CLIMATIC AREAS [April i«, 



measure both the plants dealt with and their environmental condi- 

 tions. Since both plants and their surroundings are ahvavs chang- 

 ing, it is essential that our measurements take the form of summa- 

 tions or integrations. It is therefore first incumbent upon us to find 

 means of integrating or summing the various fluctuating conditions, 

 within and without the plant body, that determine the development 

 of the organism and that decide whether it can exist at all in any 

 given set of surroundings. 



Measurement and summation of conditions within the plant. 



Our very meager knowledge of plant dynamics would render 

 quite hopeless, for the present, any attempt to integrate the qualities, 

 intensities and durations of physiological processes, were it not for 

 the fact that the plant itself furnishes at any instant a very clear and 

 unequivocal summation of the effects of all the processes which have 

 gone on in its body during its previous developmental history. This 

 fact furnishes the criterion by which comparisons have usually been 

 made between the growth processes of different kinds of living 

 things. The amount of growth accomplished during a given time 

 period may be determined by weighing the crop or some portion of 

 it, a method commonly in use in agricultural studies. Another 

 method, employed mainly by phenologists, has been to determine the 

 length of time which may elapse during certain developmental 

 phases of the organism. Thus may be determined the length of the 

 time period that intervenes between seed germination or the first 

 swelling of lead buds, and flower production or the ripening of fruits. 

 Still more simple and more easily applied is the method which merely 

 determines whether or not given plant forms are able to carry out 

 their life cycles under the environmental conditions of certain locali- 

 ties. For the positive answer to this question mere observation fre- 

 quently suffices, for its negative answer, experimentation, or at least 

 instrumentation, is necessary. If a plant form is observed as thriv- 

 ing year after year and generation after generation in a certain 

 locality, it is, as has been mentioned elsewhere, no less than redun- 

 dant to point out this as an "adaptation"; but if the given form is 

 not to be observed in this locality, the most direct and final wav to 



