standley: floras of new Mexico and Argentina 237 



blance of many of the species to others of the same genera 

 with which he is familiar in New Mexico. A comparison of the 

 flora of this limited area with that of the Rio Grande Valley of 

 New Mexico may be of some general interest. It is not certain 

 that the flora of this particular region of the southwestern United 

 States is the one with which that of the Rio Negro might best be 

 compared; but the writer, being more familiar with the vegeta- 

 tion of the Rio Grande Valley, is better able to use it as a basis of 

 comparison, than some similar area in Arizona or southern Cali- 

 fornia with whose flora, also, that of the Argentine region shows 

 an equally close or possibly even closer alliance. 



Rio Negro is sitfiated in southern Argentina, in about latitude 

 39°, upon the Rio Negro, one of the larger streams of the region. 

 The Mesilla Valley of New Mexico, with which it is proposed to 

 compare its flora, lies along the Rio Grande in southern New 

 Mexico, in latitude about 32° North. Judging from the data 

 available from Mr. Fischer's notes, the two regions must bear a 

 strong resemblance topographically : a wide river valley with large 

 areas of heavy clay soil under irrigation, broken by stretches of 

 sand dunes, the valley bordered by elevated sandy mesas or low 

 hills. In the Argentine region part of the uplands appears to 

 consist of clay soil, but in New Mexico all the mesa land is 

 sandy, at least until the foothills of the mountains are reached. 

 From the information at hand it is not possible to compare the 

 composition of the corresponding zones of vegetation; conse- 

 quently it seems more practicable to compare the related specific 

 elements which constitute each flora as a whole. 



It is remarkable to find that several species of plants are actu- 

 ally common to these two regions. These are as follows: 



Agrostis verticillata Vill. 

 Andropogon saccharoides Swartz 

 Echinochloa zelayensis (H. B. K.) 



Schult. 

 Eragrostis cilianensis (All.) Link 

 Festuca octo flora Walt. 

 Paspalum distichum L. 

 Phrag mites phragmites (L.) Karst. 

 Polypogon monspeliensis (L.) Desf . 

 Cyperus inflexus Muhl. 

 Eleocharis palustris (L.) R. Br. 

 Juncus mexicanus Willd. 



Rumex persicarioides L. 

 Monolepis nuttalliana (Roem. & 



Schult.) Greene 

 Silene antirrhina L. 

 Halerpestes cymbalaria (Pursh) 



Greene 

 Dancus pwsillus Michx. 

 Heliotr opium curassavicum L. 

 Petunia parviflora Juss. 

 Solatium elaeagnifolium Cav. 

 Linaria canadensis (L.) Dum. 



