38 VEGETATION OF A DESERT MOUNTAIN RANGE. 



Enough has been said to show that both the specific and generic 

 relationships of the Desert flora are with the desert regions of Mexico, 

 the deserts of Argentine and Chile, and even with the moist tropical 

 regions of South America. The plants which dominate the Desert 

 landscape in southern Arizona are members of genera, or even of 

 species, which characterize a much greater area to the south than to 

 the north, and they are in the main members of genera which reach 

 their maximum development in number of species and in abundance 

 of individuals in similar desert regions. The plants of the Desert which 

 are of tropical relationship are usually the sole and northernmost repre- 

 sentatives of families or genera which are much more richly represented, 

 both in types and in individuals, in the tropical zone. These plants 

 are often so infrequent and inconspicuous as scarcely to interest the 

 student of vegetation, except for the fact that their seasonal behavior 

 and habitat relations are such as to give them the most moist conditions 

 which the Desert affords. Among them may be mentioned : Passiflora, 

 Stemodia, Maurandia, and Rivina. 



The few members of genera of northern dominance, such as Populus 

 and Salix, or Anemone and Delphinium, are either to be sought in the 

 vicinity of streams and ponds, as is the case with the former two, or 

 are to be found in activity only in the late winter and early spring, as 

 is true of the latter two. The still fewer species of transcontinental 

 range are almost solely palustrine plants, as Cephalanthus occidentalis, 

 Scirpus americanus, Cyperus diandrus, and others, and are to be found 

 only in palustrine situations in Arizona. 



THE ENCINAL FLORA. 



The type of vegetation which is designated as Encinal in this paper 

 is found throughout southern Arizona and New Mexico at elevations 

 of 5,000 to 7,000 feet. It is pre-eminently a community of evergreen 

 oaks and nut pines, with many sclerophyllous shrubs. With many 

 floristic modifications this type of Encinal extends into western Texas, 

 Colorado, and inner California, usually as a belt connecting the treeless 

 plains or desert with the forested mountain tops. Encinal similar to 

 that of southern Arizona is found throughout the mountainous portions 

 of Sonora, Chihuahua, Sinaloa, and Zacatecas, and with many modi- 

 fications it extends still further south. 



The dominant species of the Encinal of the Santa Catalinas range 

 far to the south along both sides of the Sierra Madre, whereas but few 

 of them range further north than the southern edge of the Mogollon 

 Plateau in central Arizona, and some of them not even so far as that. 

 The 14 commonest woody or semi-succulent perennials in the Encinal 

 of the Santa Catalinas are all plants of extended Sonoran and Chi- 

 huahuan distribution; all of them occur in southern New Mexico and 

 eight of them in western Texas. Only one of the plants reaches Call- 



