Change of Aspect with Altitude. 237 



upper altitudinal limit. In a previous paper * the writer 

 noted the behavior of Lippia wrightii in this respect. Since 

 then other species of the desert mountain ranges of Southern 

 Arizona, have been found to exihibit the same distributional 

 character. 



The second plant found to behave similarly was Calliandra 

 eriophylla. On Tumamoc Hill, near Tucson, this dwarf shrub 

 is found sparingly in places of good soil moisture conditions, 

 preferably on north aspects. It is more adundant on rocky 

 north slopes in the foothills of the Tucson mountains, associating 

 with Selaginella. One thousand feet higher, as for instance near 

 the Sierrita IMountains, and in similar country of the same altitude 

 elsewhere, it spreads abundantly over the plains and foothills. 

 Rising another thousand feet, it was found in the Oro Blanco 

 Mountains on the timberless south side of the high hills, often 

 coming well down into the oak scrub, but leaving the opposite 

 side to the oaks. Similarly, at the same elevation of 4,500 feet 

 in the Santa Rita IMountains, it is associated with Mimosa 

 dyscoarpa on a slope falling southward into Sawmill Canyon, 

 while the north side of the ridge is given to the oaks and Nolina. 



The herbaceous perennial Perezia wrightii is found on the 

 north slopes of Tumamoc Hill at an elevation of 2,500 feet, a 

 closely related plant (P. thurhsri) was found in the Chiricahua 

 Mountains at 5,800 feet elevation at the southern base of a cliff. 

 Equally infrequent as in the preceding locations, the latter was 

 encountered in the Rincons at 4,900 feet on a west slope. 



Although annuals are frequently of wider vertical distribu- 

 tion than perrennials,and not so closely limited to special habi- 

 tats, a similar case appears to be found among the former in 

 Lupinus kptophyllus. Near Tucson it is abundant on the north 

 side of Sentinel Hill, but absent from the south side. In the 

 the Oro Blanco Mountains, it was seen growing on the south 

 side of mountains near 5,000 feet, and collected on canyon bluffs 

 of similar aspect at about 4,000 feet just acrosss the Interna- 

 tional Boundary. 



In the Santa Catalina Mountains, decending from Oracle 

 Ridge on the Leatherwood Trail, on a slope of schistose granite, 

 the physiognomy of the forest growth on a protected southerly 



♦ Plant World, XI, p. 117, June, 1908. 



