196 THE PLANT WORLD 



having an enormous range since it is to be found on the slopes 

 of the Santa Catalina mountains at 4000 feet, and on suitable 

 exposures, has been seen far to the southward among the Pin- 

 acate volcanoes in Sonora nearly down to sea level. The aro- 

 matic secretion on the stems mixed with grease or tallow has 

 long been used by the Indians and Mexicans as a salve. 



One of the wild tobaccos, Nicotiana trigoHOphylla, 

 perches among piles of rocks or on the edge of escarpments, 

 and its creamy yellow flowers open early in February. A 

 second species is more widely distributed along the washes 

 and lower slopes, and is used for smoking by the Indians of 

 the region. The third representative of the tobaccos is found 

 in Nicotiauci glanca, nati\e to South America, which has 

 found its way over the western part of the northern conti- 

 nent, being a veritable tree weed, being known to the Mexi- 

 cans as the San Juan tree. Although coming into bloom in 

 "the winter it forms flowers during any part of the year in 

 which it receives suflicient moisture. 



Verbena cUiatci grows in low clusters, and the individuals 

 in any locality show a range of variation of flower-color from 

 deep pink to pure white, while the flowering season is ended 

 only by the spring drouth. The creosote bush, Covillea tri- 

 dentata, begins to open flowers and make new leaves in Feb- 

 ruary which continues for two or three months. On the mesas 

 and sandy washes the composite Bailey a midtiradiata opens 

 numerous yellow flowers from its clumps of stems, that last 

 with their brilliant yellow effects for many days. Low and 

 decumbent on the hill slopes are the crooked branches of a 

 small shrub, CaU'uiudra eriopJiylla, which forms clusters of 

 flowers of a delicate pink and soon matures its fruits, while a 

 second species of the genus, less inconspicuous, abounds on 

 the lower mesas. 



The greater number of these perennials cast away their 

 leaxes with the approach oi the high temperatures of April 

 and May, and the stems, bulbs or root-stocks, go into quies- 

 cent condition from which they do not awaken until the fol- 



