1912] 



WATSON— PLANT GEOGRAPHY OF NEW MEXICO 



203 



the 



trail conserves the moisture after the principle of dry-farming. 



In 191 



summer rains commenced in late J 



that survived are thrifty and show abundant bloom. 



mesa is mono 



miles 



Opuntia fr 

 r (Opuntia 



see only a few grasses, Gutierrezia, 

 r occasionally a Yucca glauca or a 





..... 



■w. 





- .< ■ »»" 



V- 



MP* 



mg 









**** 



I 



■ 





Fig. i. — The head of an arroyo on the edge of the mesa: in the foreground, 

 Guticrrczuu Salsola, and Yucca glauca; to the extreme left a clump of Chrysothamnus 

 Bigelovii; in the distance the Guticrrezia association. 



The plants of the mesa belong to three ecological groups. (1) 

 Plants like the cacti, Bigelovia, Yucca, Sarcobatus, and Suacda, 

 which have large, usually underground stems or roots, in which 

 moisture is accumulated. (2) Annuals and perennials with under- 

 ground stems, including by far the largest number of individuals. 

 but usually not the largest and most conspicuous. They are 

 plants which are able to wait for the rains and then to make an 

 exceedingly rapid growth and maturity. Here belong most of the 

 mesa herbs and grasses. The latter cure perfectly in situ and 

 make most excellent hay. It is this property of the grasses that 

 makes the grazing industry possible in this country. (3) The 

 third class includes a few plants that are winter annuals. The 



