8 



The Plant World. 



times of the remarkably low stature of three feet, the whiteleaf 

 oak (Quercus hypoleuca) is only second in abundance nearly 

 everywhere except upon the most barren sun-lit rocks facing 

 southerly and westerly. It is here that the Tourney oak {Quercus 

 toumeyi), common in many places, but rarely taking the form 

 of a tree, attains especial prominence as a constituent of the 

 otherwise purely manzanita chapparal. 



A second surprise consisted in the finding of the Arizona 

 Five-leaved pine (Pinus arizonica) common quite below its 

 usual limit, even on the most exposed rims of this interesting 

 terrain. In such places it grows singly and scattered, and is 

 of rather singular habit and form. But on north and east aspects, 

 facing the swales and gullies of the interior of the mesa, it be- 

 comes the dominant species with as many as 50 to 100 trees 

 per acre, running from 8 to 16 inches in diameter, and producing 

 in places almost a true "forest floor." Usually, however, there 

 is what is known in forestry as an " understory " of whiteleaf oak 

 about 10 feet in height, interspersed with tussocks of coarse 

 mountain grass and occasional Yucca macrocarpa. 



As usual in similar places, we find Pinus chihuahuana the 

 dominant pine on some of the more open, grassy, gentle, westerly 

 slopes of deeper soil, while in steeper and more sheltered situations 

 it is conspicuous by its absence. The Mexican pinyon {Pinus 

 cembroides) is a rather prevalent species, which might suggest 

 certain conditions in common with those governing a limestone 

 flora, of which it is frequently the most prominent species. It 

 has a habit of snuggling into thickets of cypress, making tiny 

 groves with a real forest floor on sunny and rocky south and 

 west aspects, and often grows singly or in clusters about the 

 most exposed and barren rocks, a habitat nevertheless entirely 

 at variance with that which it seeks on calcareous soils of like 

 elevation. 



The cypress (Cupressus arizonica), proved the best surprise. 

 Not seen off* this mesa, except in a few isolated groups or single 

 trees, it was stumbled upon all at once growing as a body of 

 young trees in a dense narrow strip running east and west, 

 evidencing its prolific seed-bearing habit. Whether or not the 

 direction of the prevailing winds had anything to do with this 

 peculiar occurrence, this happens to be from west to east, as 

 is shown by many trees storm-warped and leaning eastward on 



