igi2] 



WATSON— PLANT GEOGRAPHY OF NEW MEXICO 



209 



grasses here, as there, are species of Andropogon, and mixed with 



them are Liatris punctata, Ratibida columnaris pulcherrima, and 

 Zygadenus. 



streams 



takes almost entire possession of the soil, forming a quite distinct 



association. 



Fig. 5. — Top of Sandia Mountains: white oaks occupying a depression where 

 they are sheltered from wind. 



In the Sandia Mountains the white oaks are very characteristic 

 of this formation, but in the more mesophytic Jemez Mountains, 

 and also on Mt. Taylor, where the yellow pine grows even more 

 luxuriantly, there is much less oak, and Merriam states that none 



was 



seen on the San Francisco Mountains, although Cowles 



reports its occurrence upon the southern slopes. The explanation 

 of this varying amount of pine and oak is to be found in the fact 

 that the oak is able to grow in more xerophytic situations than 

 the pine (fig. 5). It, with Robinia neo-mexicana and bearberry 



