322 ' BOTANICAL GAZETTE [November 



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sure; past and present extent of the forests and their present move- 

 ment, including deforestation and reforestation. The time spent 

 in the investigations upon which this paper is based includes the 

 summers of the years 1902 to 1905 inclusive. ^ 



Introduction 



The methods which I have employed are given in detail in a recent 

 work, Research methods in ecology^ by Dr. F. E. Clements, and 

 are therefore treated here verj^ briefly. They include the use of a 

 Draper psychrograph and thermograph, a geotome, aneroid barome- 

 ter, maximum, minimum, and ordinary thermometers, egg-beater 

 psychrometcrs, and a simple photometer. 



A set of the Draper instruments was established in Boulder, at 

 an altitude of 1620^, and at timber-line on the east slope of the 

 Continental Divide at an altitude of about 3420"^. A set of records 

 of these instruments was taken between June 21 and July 20, 1905. 

 The instruments were set each week by comparison with a watch and I 



with the humidity and temperature readings obtained from the egg- 

 beater psychrometer and the thermometer. The thermograph records 

 were found to agree within a few degrees with the temperature 

 as given by the thermometer, but very little confidence can be placed 

 in the psychrograph records as the reading recorded by this instru- 

 ment seldom, if ever, tallied with the readings given by the hand 

 psychrometer, and in fact the two psychrographs when running side 

 by side did not agree with each other closcrthan seven per cent. 



A set of maximum and minimum thermometers was placed at 

 the mouth of a small canon at an altitude of 1710"^ and readings 

 taken weekly from June 23 to July 31, 1905. From August 4 to 

 September 4 these were stationed on a moraine in open pine timber 

 at an altitude of 2550"^. Another set was kept on the open plains 

 three miles east of Boulder at 1590°" altitude from the middle of 

 June to the end of September.^ 



With the geotome, two soil cores were obtained at each station, 

 one of the first 11.25*="^, and one from 11.25 t^ 22. 5^"" in 



^ See below. 



3 The thermographs and psychrographs were elevated about t . 2^ above the 

 ground, the maximum and minimum thermometers 0.6™. They were all carefully 

 housed so as to protect them from the sun and yet afford free access to the air. 



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