SOIL TEMPERATURES AND VEGETATION. 



V\ I>ANii;i. Tkkmui.y MAcI)(if<iAi,. 



A committee ou the relations of plants to climate was ajj- 

 pointed at the New York meeting of the American Association 

 for the Advancement of Science in June, I'JOl, to which was 

 delegated the task of carrying out some work uj^on the rela- 

 tions of plants to various climatic factors. The actual inves- 

 tigations planned by the committee wei'e entrusted to the 

 autlior for execution, and a set of thermographs -was jiut in 

 action in northern Idaho in the summer of the same year in 

 addition to the battery that was installed in the New York 

 Botanical Garden. During the following year some tliermo- 

 metric observations were made in the Mission Mountains and 

 Kootenai Mountains,, in northern Montana, and a j^aper was 

 presented at the meeting of the Association in Denver, August, 

 1901, describing a method of estimating the total temj^era- 

 ture exposure of a plant which Avould be specially ajJiilicable 

 and useful in measuring the iuliuence of temj^eratui-e uj^on the 

 shoots of plants. 



The basal portions of a typical plant, often the larger part 

 of the body, are imbedded in the soil at various dejiths, and 

 no adequate study of the influence of temperature upon phys- 

 iological processes could be made until some accurate, grajjhic, 

 and convenient method was devised for taking continuous 

 records of the soil. The committee was given a second grant 

 by the Association, and additional funds were also voted at 

 the Pittsburg meeting in July, 1902. By the aid of additional 

 contributions from the New York Botanical Garden efforts 

 were made to devise an instrument that would meet the above 

 needs. The committee was so fortunate as to enlist the active 

 interest and practical cooperation of Prof. "William Hallock, of 

 Columbia University, who undertook to design a thermograph 

 that would make a continuous record of the soil at any desired 

 depth. A single working model was constructed in the autumn 

 of 1901 and was tested for several months in Professor Hal- 

 lock's laboratory before being installed in the Botanical Gar- 

 den, May 2, 1902. A description of this instrument, together 

 with the records obtained for May, 1902, have already been 

 published.^ It will be profitable to repeat this description 

 hei'e, together with the accompanying illustration (see fig. 1). 



The thermal element of the instrument consists of a copper 

 bulb or globe 11 centimeters in diameter (fig. 1, A), -^dth a 



^ MacDougal. The temperature of the soil. Journal of the New York 

 Botanical Garden. 3: 125-131. July, 1902. 



