SHORTER ARTICLES AND DISCUSSION 



DISTRIBUTION OF THE CACTI WITH ESPECIAL REF- 

 ERENCE TO THE ROLE PLAYED BY THE ROOT 

 RESPONSE TO SOIL TEMPERATURE 

 AND SOIL MOISTURE 



As is very well known, it is the common habit, when referring 

 to the relation of a "plant" to its environment, to mean the sub- 

 aerial portion only, leaving quite to one side the subterranean 

 parts. That there is little logic in this will be readily acknowl- 

 edged, although the possible causes are not far to seek. In the 

 first place, for patent reasons, roots do not greatly excite our ad- 

 miration or curiosity, and thus have received little attention in 

 the field. Further, relatively little experimental work has been 

 done on the roots of plants other than on seedlings and growing 

 in solutions. And besides these conditions which refer immedi- 

 ately to the plant, there is a nearly related one which has to do 

 with its environment, especially with the root environment. The 

 soils and the soil condition of whatever sort are probably more 

 difficult to study, and the results more difficult to express in a 

 manner capable of ready application than the subaerial environ- 

 ment of the plant. However, it has not been its difficulty alone 

 that has been the deterrent in the study of the environment of 

 roots since certain features, for instance the soil temperature, can 

 be easily learned by appropriate apparatus. Could we have a 

 comprehensive series of data touching this feature alone, to men- 

 tion no other, we should be in possession of a very useful engine 

 for use in comparative studies on causes underlying the distribu- 

 tion of plants, and, further, through it the study of the root- 

 systems of plants, and of their biological value, would be greatly 

 stimulated. 



While it is here recognized that the presence of a plant in its 

 environment is an expression of the response of the whole plant to 

 the entire environment, it is necessary, for the purpose m hand, 

 to ignore the responses of the shoots, and to focus our attf-ntion 

 for the time on the root relation alone. It can be noted, however, 

 as is very well known, that the activities of the latter may be 

 reflected in those of the former. Such a condition, having inter- 

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