BOTANICAL GAZETTE. 115 



height of 7,000 to 8,000 feet. It continues to rise as we trace %\ 

 southward into California, being on Shasta and the neighboring 

 mountains 8,000 feet above the sea. On the high sierras of Eastern- 

 central California, forests grow to 10,000 or 11,000 teet, while the 

 San Bernardino and other ranges of Southern California do not 

 reach the upper limit of Jforcsts, 



Few of the ranges of Nevada reach the timber line, which is 

 at a height of 9,000 feet in the north up to, probably 11,000 feet in 

 the southern part of the State. 



In Arizona, probably none of the mountains reach the timber 

 line, except the volcanic group known as the San Francisco Moun- 

 tains, and the Sierra Blanca. On these the timber line is between 

 11,000 and 12,000 feet. 



In New Mexico, it averages about 12,000 feet above sea level. 

 There is little variation between the northern and southern parts 

 of the territory, as the higher annual temperature of the southern 

 part is fully compensated for by the greater altitude of the plateau 

 m the northern part. 



In Colorado, it ranges from 12,000 feet in the southern part to 

 11,000 in the north. It is highest in the great mass of the San 

 Juan Mountains and in the Sangre de Cristo range, and lower in 

 the northern portions of the Park and Front Ranges. 



In Southern Wyoming, in the Park range, which is the only 

 one in this portion of the territory which rises above the limit of 

 timber, this limit is at about 11,000 feet. In the Wind River and 

 Teton Ranges, in the northwestern part of the territory, it is at an 

 elevation of 10,000 to 11,000 feet._ 



In, Montana and Idaho, the limit of timber is, in general, from 

 9,000 to 10,000 feet, being highest in the south, and lowest near the 

 northern boundary. 



In the Uinta and Wahsatch Ranges of Utah, it is about 10,000 

 feet rising somewhat above this figure in the southern part of the 

 latter range. 



Thus it is seen that in the same latitude, there is a very 

 marked difference in the height of the timber line. The less the 

 elevation of the surrounding country, other things being equal, 

 the iower is the limit of timber. 



This suggests a farther point. The upper limit of timber 

 must have approximately the same mean annual temperature 

 everywhere. Of course it will differ to a slight extent in different 

 localities, owing to difference of exposure to wind and sun, but 

 these are mere local circumstances, not effecting the general princi- 

 ple. The determination of this temperature accurately is, with- 

 out direct observation, of course, impossible. I have, however, 

 computed it approximately from such data as are available, and 

 have found tolerably close accordance among the results. 



The mean annual temperature decreases about 1° Fah. for each 

 300 feet of abrupt ascent. In the case of Pike's Peak and 



