1919] Hall: Chrysotlnnnnus nmiseosus and Its Varieties 163 



species. Every other character tried, such as size or shape of the 

 leaves or of the parts of the involucre or flower, the nature of the 

 pappus or style-branches, and the pubescence of the akenes, have all 

 been found to be even more variable and not to serve well as a basis 

 for a natural classification. Moreover, the pubescent involucre is 

 nearly always associated with a white or grajdsh appearance of the 

 foliage so that the use of this character divides the whole species into 

 two series of varieties, which series may, for the most part, be recog- 

 nized by their general appearance. 



After the foregoing remarks as to the variability of characters in 

 this species it will perhaps be understood that one cannot expect to 

 use the key to varieties with entire satisfaction. The large number 

 of intermediate forms and the numerous permutations of characters 

 render it impossible to prepare a key whereby one may definitely 

 identify every specimen that comes to hand. It is believed, how- 

 ever, that with the exception of one or two little-known forms of 

 eastern Oregon and Washington, all of the major variants have been 

 accounted for. 



This study has been greatly facilitated through the assistance of 

 a considerable number of people but since these will be specifically 

 mentioned in the report on the rubber plant investigations the list 

 need not be given here. AcknowledgTuent should be made at this 

 place, however, of the kindness of Dr. B. L. Robinson, of the Gray 

 Herbarium of Harvard University, and also of that of Dr. P. A. 

 Rj-dberg, of the New York Botanical Garden, in permitting the 

 author to examine certain type specimens in their charge. Further- 

 more, Dr. Aven Nelson has made available the rich collections of the 

 Rocky Mountain Herbarium at the University of Wyoming. 



II. KEY TO THE VARIETIES OF CHRYSOTHAMNUS 



NAUSE0SU8- 



Series A. The Gray Forms 

 Involucres tomentulose (at least the short outer bracts) to densely woolly: 

 foliage mostly gray or even white with a rather copious pubescence, this either fine 

 and close or floccose-tomentose (least pronounced in oreophil'us and speciosus). 



Akenes densely strigose. 



Tomentum loose, copious, and nearly pure white on twigs and leaves, extending 

 to the iuvolucies: corolla-tube nearly always arachnoid-pubescent. 



-See also doubtful forms on p. 180. 



