Atmospherical Influences 63 



uninitiated, appear as the true source of the disease, are' 

 merely the result of the unfavorable physiological condi- 

 tions of the tree. 



Hence in diagnosing, one should never be satisfied to 

 stop short of an examination of the condition of the patient 

 in all directions. 



Atmospherical Influences. The conditions of the atmos- 

 phere naturally also influence the functions of the tree, but 

 are mostly not under control. Here, too, species vary in 

 their requirements and in their capacity for adaptation. 

 Here even more than with reference to soil conditions (which 

 are under control) it is necessary to make sure of the natural 

 adaptation of the tree to its surroundings. And, we reit- 

 erate, it is not only the species that need consideration, but 

 the individual itself, when transplanted from one set of 

 conditions to another. For, the individual tree as it grows 

 up from the seed has the capacity of adjusting itself to its 

 'environment, but when suddenly transplanted into other 

 surroundings it cannot do so at once. Hence it may be 

 ailing for some time until it gradually adjusts itself, or else 

 it may succumb to the unaccustomed conditions, either 

 directly or by physiological disease, or indirectly by falling 

 a prey to parasites in its enfeebled state. 



If, in planting, species or specimens have been chosen 

 which are adapted neither to the conditions of humidity or . 

 drouth, nor to the temperature changes of the atmosphere 

 common in their new home, they will suffer, and perhaps 

 die, and should be replaced by those which are better suited 

 to the environment. Theoretically, it niay be possible to 

 help such exotics by regulating the soil conditions, and to 

 mitigate climatic conditions by screens and other protec- 

 tion; but practically this is usually too troublesome. 



Soil and atmosphere are in such interdependence as far 



