160 I'liiiursili/ of California I'liblicutiotis in Botanij | Voi- 7 



is pcrluips till' most sat isfiH'tory result ot" all of the iiiiincroiis a1t(iii|)ts 

 to set up genera in this <iroii|) where generic limits are admittedly 

 most diffieult to estahlish. 



Within the genus we find a multitude of natural forms of greatei- 

 or li'ss siguitieanee. This has led botanists greatly to increase tlie 

 num])er of si)eeies and vai'ieties, so that not less than one hundred 

 and thirt<'en of these have been described and this numbei- could l)e 

 multij)lied several times through more extensive field studies and 

 witliout the employment of characters other than those alreadx' pro- 

 posed for the basis of species. This is partly because these single 

 characters have been vai"iously uniti'd in nature to form a largt' 

 nuiid)er of combinations, but it is also because of the extreme varia- 

 bility of some of the chai'acters themselves. The ninnerous forms of 

 Chrijsothainims may be assembled into five natui'al groups as follows: 



7\EV TO TITP: RECTTOXS of CHFYSOTHAMiXCS 



Tr('rl)aije not it'siiious-pum-tatc: leaves oblauceolate to nar- 

 rowly linear or terete. 

 Heads in leafj' spike-like or raceme-like clusters: outer 

 bracts of the involucre prolonged into a slender 



herbaceous tij) or a])pendage Section 1. Parryani 



(Principal species: Parri/i, Hownrdi.) 

 Heads cymose, paniculate, or solitary at the ends of the 

 branches: bracts obtuse to acuminate, devoid of 

 herbaceous tip. 

 Twigs not tomentose, either smooth and glabrous or 

 only scabrid or puberulent: style-appendages from 

 included to long-exserted. 

 Bracts strongly keeled, in five very distinct vertical 



ridges Section 2. Pui.chem.i 



(Principal species: pulehellus, depressii,i.) 

 Bracts scarcely keeled and the vertical ridges obscure. .Section :!. Tvpici 

 (Principal sj)ecies: <ilhidiin, (irreiici. (iroinincns. 

 Vasciji, viscidifioius. ) 

 Twigs closely covered with a pannose tomentum which 

 usually persists for several years: style-appendages 

 mostly longei- than tlie stigmatic portion and long- 

 exserted Section 4. Xaiseosi 



(Single species: dohscosu^s.^) 



Herbage resinous-punctate: leaves terete Section .">. I'i'sctati 



(Principal species: teretifolius, paniculatus.) 



Of the at)ove five grou|)s rubber has been found in more than 

 minute quantities only in the NauseosiaLwd I'unctati. Since the latter 



1 It is possilde tiiat C. formosu^ Greene and C. turbiiintu.f (M. E. Jones) 

 Rydb. constitute additional species of this grou]i. See p. ISO. 



