2o6 



BOTANICAL GAZETTE 



[SEPTEMBER 



to the mountains, but where the mesa rises higher (6500 ft. or over) 

 it stretches out over the plains. In the Estancia Valley it seems 

 to be spreading at the expense of the prairie, as considerable areas 

 are dotted over with young trees where there are no signs of old 

 ones. But in many places, as here, it clings to the rock outcrop 

 and to the neighborhood of scattered rocks, doubtless because of 

 the moisture conserved under them. In this connection it is 



■■i 



*-^W % 



Fig. 3. — Opuntia arborescens in fruit: to the left is an arroyo 



interesting to recall the occasional occurrence of cedars on the lava 



a thousand feet lower. 



ge of this formation 



moisture is evident. 

 l the lower limit of 



On the whole, 



snow. Near the lower edge, especially, the trees are far apart, 

 broken, stunted, gnarled, constantly recalling an old neglected 

 orchard in a back pasture in Ohio. Gutierrezia and Yucca glanca 

 extend into this formation and Opuntia arborescens is abundant 



