TWO RACKS OF .\>r»:N 



to make <;oino\vhai interior height i^rowth and to have rather poo \r 

 form than the "white."' ^[easurement^ in a J4-year-oUl stand on the 

 Cioiuuls ot the Great Rasin Experitnent Station show a dii^Vienco of 

 only .0;i inch in the diameter of the "white" and "yellow" trees, how- 

 over, in favor of the "white." while the finest stand in the repon around 

 the Great Basin Experiment Station is "yellow." near the upjxT limits 

 of aspen in an Engelmann spruce hum. There is really no constant 

 difference in development worthy of practical cotisideraiion. 



The cause of these two races is not clear. It seems plainly tioi due 

 to soil, or conditions of growth nor does it seem to be linked with the 

 sex of the trees. The "white" trees Bower i^staminate only) very 

 much more gxMierally than the "yellow" trees, as far as observed, but 

 'yellow" trees are also occasionally seen with catkins. Flowering is 

 infrei]ucut in either class. Pistillate Howers are extremely rare, having 

 been found for example in only one small locality in Ephriatu Canyon. 

 These few trees are "yellow " — early leating. 



In many places where the line betweeti the two forms runs out into 

 a treeless openiiig. the front of the aspen type edg^ing the opening is 

 not even, but has a considerable indentation where it is iniersec«ed by 

 the line dividing th.e two forms. The appearance gives the imi)ression 

 that the "white" trees and the "yellow" trees spread out fnMU inde- 

 pendent centers and titially joined to form one solid body. 



The writer confesses an entire inability to explain the cause of these 

 two widely distributed, but distinct and closely intermingled races of 

 aspen. This article has been written in the hope that it tnight evoke 

 commcius from others who have i\oted the same two races with dif- 

 ferent leating periods and bark characteristics, which might throw 

 further light on this iiueresting condition. 



