i ees 
The North American species of Hymenoxys 
T.D.- Av GOCKERREL 
(WITH PLATES 20-23) 
Much interest has been excited in Colorado by the discovery 
of the existence of rubber in the roots of the plant recently de- 
scribed as Picradenia floribunda utilis. It appears that sheep-herders 
have for years been in the habit of chewing the roots of this plant, 
obtaining thereby a product which served for chewing-gum. Mr. 
F. R. Marsh, of Denver, conceived the idea of turning this sub- 
stance to commercial use, and at the present time arrangements are 
being made for its extraction on a large scale. When Mr. Marsh 
presented the matter to me, asking that it should be investigated, 
I was naturally quite skeptical; but my wife undertook to make 
the necessary chemical tests, and obtained the excellent results she 
has described in Science (Il. 19: 314. 19 F 1904). 
In Colorado, the plant in question is sometimes referred to as 
rabbit-weed ; but I believe that several Compositae are confused 
under this name. Mr. E. C. Van Diest tells me that the Mexi- 
cans call it pengué, but here again it may be that two or more 
things are confused. He states that it is poisonous to sheep in the 
spring — probably on account of its mechanical rather than its 
chemical properties. 
Finding the plant of so much interest, I undertook a botanical 
investigation of it and its allies. It soon became apparent that the 
whole genus required revision, and this paper was accordingly pre- 
pared. The possibility of the undertaking has depended entirely 
upon the kindness with which several botanists responded to my 
requests for the loan of specimens, Dr. Rose sending all the 
material of the National Museum, Dr. Trelease that of the Missouri 
Botanical Garden, Miss Eastwood that of the California Academy of 
Sciences, Prof. Aven Nelson that of the University of Wyoming, 
Prof. E. O. Wooton that of the New Mexico Agricultural College, 
and his own herbarium ; and last but not least, Dr. E. L. Greene 
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