46 BULLETIN 140, U. S. DEPARTMENT OF AGEICULTUEE. 



of the sap and, therefore, ultimately on the rapidity of transpiration 

 from the leaves. And again : 



A warm summer is always accompanied by a high temperature of the ground 

 or by a rise of its temperature. The increase is the more decided the more the 

 excess in the temperature of the air is accompanied by a large quantity of rain 

 or has been immediately preceded by it. In warm and comparatively dry sum- 

 mers the rise of the earth's temperature does not perceptibly exceed the 

 normal. * * * The dampness of the soil is sufficient to allow the variations 

 in the temperature of the air in winter and spring to exercise a decided influence 

 upon those of the soil, whereas, in summer an excess of rain would be necessary 

 to accomplish this, and that, too, to a greater degree if the soil be covered with 

 vegetation. 



Quetelet, as far back as 1849, in his " Climate of Belgium," ex- 

 pressed regret that he had been unable in his crop-climate studies to 

 consider the influence of the temperature of the soil, although " it 

 is absolutely necessary so to do in order to treat the phenomena of 

 vegetation in a complete manner." 



Mr. Knight x has observed that " varieties of the same species of 

 fruit tree do not succeed equally in the same soil, or with the same 

 manure," and further, that this applies to the peach, pear, and apple, 

 " as defects of opposite kinds occur in the varieties of every species 

 of fruit,- those qualities of soil which are beneficial in some cases will 

 be found injurious in others. In those districts where the apple and 

 pear are cultivated for cider and perry, much of the success of the 

 planter is found to depend on his skill or good fortune in adapting 

 his fruit to his soil. 2 



McClatchie and Coit, 3 in discussing varieties, state that — : 



The same variety reacts very differently to the various stimuli produced by 

 different environments. Hence, we arrive at the commonly held and correct 

 idea that each climatological area has its own peculiar set of varieties which 

 succeed best under its own climate and soil conditions. 



Hence it follows that the supply of soil moisture available to plants 

 and the temperature of the soil to depth equaling or exceeding that 

 of the root zone of plants and trees, seem to account in part at least 

 for the phenomena of the soil-varietal adaptations. These two fac- 

 tors constitute the soil climate and in subsoils they are governed 

 indirectly but chiefly by the texture and structure as related to the 

 moisture supply. In the surface soil these have been or may be modi- 

 field to some extent by the addition of humus, but the latter influence 

 is entirely insufficient to control the matter of inherent adaptation 

 of soil t} r pes to crops, or to different varieties of the same crop. 



It is evident, then, that many of our crops bear testimony, both from 

 experimentation and from well-established agricultural practice, to 



1 Lindley's Theory of Horticulture. 1841. Chap. 20. 



2 Bui. 61, Arizona Agr. Expt. Sta. 



3 Trans. Royal Hort, Soc, I, 6. 



