68 • 2^Iuhlenbergia, Volume 7 



order, each characterizing b}- its range the climatic conditions 

 of its own zone. To be sure, upon reaching the crest of Oracle 

 ridge, what was to all appearances C. laxa broke into the zone 

 of C. Integra again after having once been left behind, but this 

 may have been due to exposed conditions, or else to peculiar 

 soil, since the locality is near a mineral belt. To some degree 

 the difference in climate between the three zones is reflected in 

 a corresponding difference in at least one detail of structure — 

 pubescence. C. laxa is quite hairy, C. integra has a short, fine 

 velvety pubescence, while C. aiistro7noniana is hairy only at the 

 base and in the inflorescence, mostly scabrous or barely puberu- 

 lent elsewhere, becoming almost entirely glabrous in the most 

 humid habitats. 



C. LANATA Gray, Bot. Mex. Bound. 118. 1859. 

 This strikingly handsome white woolly plant was collected 

 by Wright in the early days. Its distribution appears to be 

 southern Arizona, western Texas, Coahuila, and Zacatecas. 

 Found on a very steep south slope on Marble peak in the Santa 

 Catalina mountains, elevation 7500 feet, October 6, 1910, no. 

 3912. The late flowering may be due to the fact that the slope 

 was burned over in June. The soil here is whitish, somewhat 

 loose, and very calcareous. Recently F. E. Lloyd collected it 

 in Zacatecas, which is a limestone region. It is not improbable 

 that the species will ultimately be found limited to limestone or 

 calcareous soils. In keeping with other limestone plants, it 

 shows much more xerophytic structure than is ordinarily found 

 at this elevation. Near this species, tho possibly quite distinct, 

 is no. ?^p/, collected April 10, 1910, on a steep northeast slope 

 on the east side of the northwest spur in the Boboquivari moun- 

 tains. The elevation here is only about 4000 feet, and tlie soil 

 granitic. The exceedingly woolly character of the plant .seems 

 to be well adapted to the low' elevation. The dense tomentum 

 of the stem is slightly yellowish. . It may or ma\- not prove to 

 be C. tomentosa Gray, collected at INIabibi, vSonora, June, 1851, 

 bv Georee Thurber. 



