30 DESERT BOTANICAL LABORATORY 



near the station of Escalante south of Torres, but at Guaymas it was 

 replaced by a species of similar habit, with different fruit, Cereus 

 pringlel. A remarkable mixture of plants occurred along the beach 

 in the salt waters of the harbor where small mangroves {Avicennia and 

 Rhizophora) which we are accustomed to associate with the humid 

 tropics, grew side by side with Cerezis tJmrberi^ Ceretis pringlei^ and 

 other characteristic desert plants (Plates XXI and XXII). 



THE COLORADO DESERT. 



The Colorado desert of California offers, along the line of the 

 Southern Pacific, several types of vegetative areas, the result of soil 

 differences. West of the Colorado river bottom, in the gravel hills, 

 the creosote bush ( Covillea tridentata) is the principal woody species, 

 the tops of the ridges being so exceedingly arid as to be devoid even of 

 that most drouth resistant plant. Associated with the creosote bush 

 are the ocotillo {^Fotiquieria splendens') and the ironwood (^Olneya 

 tesota), and occasionally the mesquite {Prosopis)^ a joint pine 

 {^Ephedra)^ and a palo verde {Parkinsonia torreyand). Within 

 sight of the railroad, to the southward, extends a line of sand dunes 

 from the Colorado river northwestward for about fifty miles, nearly to 

 Flowing Well. These extensive dunes we were not able to examine, 

 but from the fact that they lie in what is probably the most arid of all 

 the deserts of North America, it is believed that their flora is well 

 worth critical geographical examination. 



At the station Volcano the alkali flats begin. At first these have 

 little white incrustations and are devoid of vegetation except for a few 

 saline plants along the arroyos, such as the chenopodiaceous shrubs 

 Allem-olfea and Suaeda. At the station Frink, i6 miles east of 

 Salton, white incrustations begin. Here in occasional areas the only 

 plant growth consists of clumps of Allenrolfea growing upon hum- 

 mocks of earth rising above the general level of the alkali incrusted soil. 



At Salton, which lies on the edge of the salt flat and near which are 

 several saline or alkaline springs, is afforded an excellent opportunity 

 for securing material of alkali resistant plants. On the sandy hum- 

 mocks desertward from the alkali incrusted soil were two salt bushes 

 {Atriplex canescens and -<4. polycarpa) , a composite bush with burlike 

 fruits ( Gaertneria dutnosa)^ a Parosela^a Stiaeda^ the mesquite (^Pro- 

 sopis)^ and an occasional Lychim and ironwood tree ( Ohteya tesotd) . 

 The springs are sluggish and have built up about themselves low 

 mounds of earth. The soil, except where the water is actually emerg- 

 ing, had an incrustation of salt and alkali. Four plants make up most 



