12 THE PLANT WORLD. 



It was my good fortune, in July, 1906, to visit this canon in 

 company with ^Ir. A. G. Ruthven of the University of Michigan. 

 We entered it at the upper end, at an altitude of upwards of 

 6,000 feet, and proceeded downward along the stream which in 

 places leaps with considerable force between the rocks, still con- 

 tributing its share to the process of erosion, the effects of which 

 are so marked on either hand. A light rain was falling, but 

 the camera was used to good purpose between showers, and the 

 day proved to be more favorable, on the whole, than one of full 

 sunshine.* 



At our first halting-place near the entrance to the canon, it 

 became evident that we were in the midst of a flora widely dif- 

 ferent from that of the hills over which we had just come. We 

 had there been walking through a low forest of pifion, PIjiks 

 cdnlis, one-seeded juniper, Jujiipcnis iiionospcniia. and the alli- 

 gator juniper, /. pachypJilo'a, all characteristic members of the 

 pinon association, which forms a zone about the mountain ap- 

 proximately 1,500 feet in vertical width at this place. Now, how- 

 ever, in the very midst of this zone, we found in the low ground 

 of the canon the white oak, wild black cherry, choke cherry, ash, 

 hop-tree, Virginia creeper, poison ivy, grape-vines, and other 

 familiar constituents of an eastern mesophytic forest, and with 

 them a few conifers, the yellow pine, white fir, and Mexican 

 white pine. These latter are more numerously represented and 

 attain a better development 1,500 to 2,500 feet higher up, where, 

 with Pseiidotsiiga ta.ri folia and Picca cngcliiiaiuii. they form the 

 fine forest which covers the higher parts of the mountain. The 

 place where we stood was their lower limit. As we proceeded 

 below the 6,000 foot level we saw no more of them ; they are 

 plainly species that at the present time belong to a considerably 

 higher altitude, but seem, through favoring circumstances, to 

 have crept dowai the canon some 2,000 feet below the zone of 

 their best development. 



Leaving the case unsettled, we turned our attention to the 

 walls of the caiion. Here was a striking picture. At our feet 

 and around us a mesophytic forest and a group of conifers that 



* I am indebted to i\Ir. Ruthven for the accompanying photographs. 



