V 



PLANT GEOGRAPHY OF NORTH CENTRAL 



NEW MEXICO 1 



CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 160 



J. R. Watson 



(with seven figures) 



F i 



The area included in this investigation comprises the northern 



i 



half of New Mexico, the most detailed study having been made of 

 Bernalillo and portions of the adjoining counties containing a 

 section of the Rio Grande Valley and the Sandia Mountains, but 

 the results have been confirmed by excursions to other portions 

 of the northern half of the territory. 



The 35th parallel passes through the region under consideration, 

 which indicates a hot sun during the summer and a warm one 

 during the winter. The altitude ranges. from a little less than 

 5000 ft. in the valley of the Rio Grande to about 11,000 ft. on the 

 northern part of the Sandia Range. 



The topography is varied. The recent valley of the Rio 

 Grande, occupying the center of our region, is two or three miles 

 wide. The floor is composed of beds of a hard clay ("adobe")' 

 sand, and gravel. The water level is here usually only a foot or 

 two below the surface and near the river often rises above it, leaving, 

 when the water evaporates, a crust of alkali which whitens the 

 ground like hoar frost on a November morning. The river is a 

 shallow, muddy stream with a fall of five feet per mile. It may be 

 a half-mile or more wide during the June melting of the snow on the 

 Colorado mountains, or entirely dry during August, under the 

 combined influence of drought and the demands of the irrigation 

 ditches above. At low water it exposes extensive mud flats on 

 which a vigorous plant growth quickly develops. 



much 



mesa, which rises 



may 



1 This study was undertaken under the direction of Dr. Henry C. Cowufis. 



Botanical Gazette, vol. 54] 



[i94 



