INTRODUCED PLANTS OF A DESERT VALLEY 279 



dance and universality in the Imperial region favor the possibility 

 that they entered it from the former source. 



Chloris elegans is a common grass in fields and about towns. 

 It grows also along the Colorado River, but in the older settled 

 parts of southern California has only made its appearance in re- 

 cent years, and as an occasional waif, introduced probably from 

 Imperial Valley. It has been considered as indigenous along the 

 southern border of the Colorado Desert, but I have seen it nowhere 

 under conditions that did not indicate that it was an introduced 

 plant. 



The remaining group of plants introduced into the Imperial 

 Valley comprises those which are more or less common in most 

 parts of southern California, but are not found in the alluvial 

 lands of the lower Colorado. They are largely cosmopolitan weeds 

 which follow the footsteps of civilized man. They have unques- 

 tionably reached the Valley through its intercourse with the older 

 parts of California. None of them are here abundant, most were 

 seen only in a few places, and some of these, which elsewhere are 

 among the commonest of weeds, are here little more than adven- 

 tive. 



Among grasses Cynodon dactylon and Paspalum distichum are 

 common in all parts of the Valley, Setaria glauca is frequent but 

 nowhere abundant, and Holcus halepensis is rare. Helianthus 

 annuus is often seen but not in quantity, Sonchus oleraceus is abun- 

 dant and S. asper occasional. Chenopodium murale, Brassica 

 nigra, Melilotus indica, Malva parviflora, Portulaca oleracea and 

 Ambrosia psilostachya were all seldom seen, and are as yet hardly 

 more than adventive. 



An interesting feature of the Imperial flora is the number of 

 common weeds of California which were not observed in any part 

 of the Valle3\ The following is a list of them: 



Amaranthus chlorostachys Bromus maximus var. 



Amaranthus graecizans Bromus rubens 



Amaranthus hybridus Capsella bursa-pastoris 



Avena barbaia Centaurea solstitialis 



Avenafatua Chenopodium album 



Bidens pilosa Chenopodium ambrosioides 



Brassica campestris Cotula coronopijolia 



