BOTANICAL GAZETTE. 125 



vice versa, and that these variable, intermediate, and unstable states 

 had sprung from acorns thus crossed. And this is the consideration 

 which I wished specially to emphasize. It is often and truly said that 

 persons unfamiliar with any special branch of natural science are in- 

 capable of appreciating the nature and force of scientific convictions. 

 This would be pre eminently true in this case. Standing in the pres- 

 ence of these forest denizens, I felt that they were si:)eaking to me and 

 revealing to me the secret of their conception, birth and life, in a 

 language more potent and convincing than any words or voice could 

 make it— Lester F. Ward. 



Timber Line in the Sawaich Range.— That part of the main 

 range of the Rocky Mountains known as the Sawatch Range has a 

 general north and south direction with spurs running east and west 

 between which the different streams find their way into the Arkansas 

 or Gunnison Rivers. 



The direction of the spurs and range is important, as by it the 

 height of the tree line is in great part determined. 



Timber line is generally at an altitude of nearly 12,000 feet above 

 sea level, but in some localities may be lower than 11,000 feet. Picca 

 Engclmauni {oxm'i the great mass of the forest at high altitudes, some- 

 times Finns aristata is quite i)lenty and in some places there are a few 

 trees of Pinus flexilis and rarely the Aspen comes to be a member of 

 the high alpine woods. 



Close to timber line are found the largest trees and most magnifi- 

 cent forests of Engelmann's Spruce and there is not the gradual 

 decrease of size and vigor that the cold of an arctic climate should 

 cause. 



A few steps and one passes from a dense forest to a treeless 

 region extending to the summits. 



Engelmann's Spruce will not grow on the rocky slides so common 

 in the Rocky Mountains, nor in a very wet location, but an excess of 

 moisture does not influence the altitude of timber line. 



Most of the summits of the very high peaks, such as Antero, 

 Ouray and Princeton, are nearly clean rock, surrounded by "slides," 

 and their tree- line is determined by conditions of soil; and many ( f 

 the lesser peaks also have an apparent tree limit caused only by rocky 

 summits. 



The scattered trees finding a foot hold on the steep sides of such 

 peaks, not having the protection against the elements, that in a forest 

 one tree gives to another do not grow at as high an altitude as the soil 

 would permit. The main agents in preventing the forest from cross- 

 ing the "divides" are the snow and wind. 



Some idea of the jjower of snow at high altitudes may be imag 

 ined by noticing the paths of the "snow slides," or avalanches, swept 

 clean of trees from ilie summit to the base. At one place near Mt. 

 Antero, where an avalanche had come down, the trees from the 

 mountain side were piled up twenty feet high for a distance of five 

 hundred feet. Near tree line, where there has been no downward 



