An Arizona Mesa. 



9 



the peaks and passes of the main crest. Absent on more shel- 

 tered places, the cypress became more and more abundant west- 

 ward (a significant direction) especially on the rockiest, most 

 inhospitable situations. Indeed, over large areas here, except- 

 ing the secondary pinvon, it produced the only tree growth, in 

 the form of well-nigh impassable brakes and for the first time 

 was seen in what appeared to be its thoroughly native and long- 

 established habitat. Many other facts were gathered which 

 indicate that if any tree species of this region is worth watching 

 from the standpoint of plant movement, it is this one. 



The Arizona Longleaf Pine (Pinus mayriana) is unexpectedly 

 rare, for only two or three trees were seen. In similar altitudes 

 a few miles away, on andesite, it is a common forest tree. But 

 conditions in this case do not admit of comparison in a way to 

 fix the exclusive responsibility upon the origin of the rock and 

 soil, as can be demonstrated in other places with other species. 

 The alligator juniper (Juniperus pachy phloea) , though present, 

 is rather infrequent and solitary, its usual habit of occurrence, 

 and on the barren manzanita flats and slopes, altogether absent. 

 Quercus reticulata is occasional as another unusually small shrub 

 on high, dry places, but becomes more frequent and larger in 

 some parts of the sheltered draws. Quercus arizonica was met 

 only infrequently, though this is often the very altitude of its 

 best development otherwise. Garrya wrightii is somewhat 

 rarely present, for only two bushes were seen. The mountain 

 mahogany (Cercocarpus parvifolius paucidentatus) was not en- 

 countered at all. Both are prominent shrubs on the limestone 

 near by. Quercus emoryi is also practically absent, one or two 

 small specimens having been noted. The reason in this case is 

 evidently to be sought in the lower altitude to which this oak 

 belongs. Clumps of Bear grass (Nolina erumpens) are present 

 occasionally, the smooth and handsome Yucca macrocarpa 

 rather more frequently, and two species of Agave were seen two 

 or three times each. The trip being made in November, only 

 the larger perennials were in evidence. 



It was evident that several peculiarities marked this pla- 

 teau from the usual mountain slopes in the neighborhood, 

 though the degree of isolation is not great. It is possible that 

 when such land forms when widely separated are more inten- 

 sively explored they may yield results in the way of comparative 



