CRITERIA. 167 



western Nevada and northwestern California have generally longer involucres and 

 corollas than those from farther east. 



The position taken by the corolla-lobe is of some interest. Long lobes are inclined 

 to spread or even to recurve ; short lobes are usually erect and in some cases are connivent 

 around the stamen-tube. Such extremes are sometimes found within a single species, 

 as in C. nauseosus viridulus and C. n. gnaphalodes. 



The pubescence of the corolla exhibits some striking variations, without offering any- 

 thing of more than subspecific value. The tube is either glabrous or minutely puberu- 

 lent, even in plants belonging to the same variety. Quite different is the additional long 

 arachnoid pubescence that appears on the tube of some subspecies of nauseosus. This 

 consists of loose, crooked hairs often 1.5 mm. long. Such pubescence would be of much 

 diagnostic value were it constant and if it did not occur in varying amounts. Among 

 specimens referred to a broad-leaved form of subspecies speciosus of this species, some 

 have abundantly arachnoid-pubescent corolla-tubes {Hall 10853, Heller 7192), while 

 others are almost identical with these in all respects, except that the tube has only the 

 usual crisp pubescence common throughout the genus (Univ. Calif. Herb., 87248, 31163). 

 Similarly among fairly uniform collections of subspecies typicus, the tube is found to be 

 either essentially glabrous (Howell Lakes, Wyoming, Nelson 5315), or short-hirsute 

 (Laramie, Wyoming, July 29, 1889 Greene), or more rarely arachnoid-pubescent 

 (Laramie, Wyoming, Nelson 2787). In subspecies hololeucus the long hairs are usually 

 very conspicuous. However, among apparently identical plants growing within a few 

 meters of one another, some will be found to have a copious pubescence, others a scant 

 amount, others none at all (Benton, California, Hall 10654). In other collections of 

 hololeucus the long hairs will be only 2 or 3 in number {Hall 10610) or entirely wanting 

 on plants a few kilometers removed. The tips of the corolla-lobes are sometimes con- 

 spicuously long-hairy. This character is constant for C. parryi lalior as far as indi- 

 cated by the few collections at hand. In C. nauseosus it constantly occurs only in 

 subspecies turhinatus and junceus. In the latter it is of but little value, for the hairs 

 are few in number and deciduous. The lobes of C. nauseosus bigelom are usually glab- 

 rous, but in one collection they vary from sparsely to copiously villous {Hall III40 UC). 

 In the Mexican C. pyramidaius the lobes are puberulent at the tip. It seems, there- 

 fore, that the pubescence of the corolla-parts furnishes criteria of doubtful specific 

 value, but of some use in the segregation of minor forms and as a clue in tracing the 

 lines of evolution. 



Number of flowers in the head. — Aside from C. parryi and C. pyramidaius the number 

 of flowers is almost constantly 5. As one would expect, this number occasionally drops 

 to 4, or more often it increases to 6 or 7. In C. parryi, however, the heads have more 

 numerous flowers, and here the character is of some importance for recognition of sub- 

 species. In fact, it has been heretofore considered specific as between parryi and howardi, 

 but the series of counts enumerated in table 22 indicates very clearly that it can not be 

 used for this purpose, especially when the other subspecies are taken into account. 



Involucre. — In common with most other Compositae, the involucre of Chrysothamnus 

 offers characters of considerable importance. The bracts are arranged in 5 more or less 

 evident vertical rows. When these ranks are well defined the involucre is sharply 5- 

 angled; when they are obscure it is more rounded and without definite angles. The 

 number of bracts in each row varies from 3 to 5, there being a tendency in each species 

 toward either the smallest or the highest number but with no absolute fixity. Such char- 

 acters as these are of much service in arriving at conclusions as to specific or sectional 

 limits when a large series of specimens are at hand for comparison, but being relative 

 they are difficult of application when one is making determinations from keys and 

 descriptions. The shape of the scales themselves is also of value. It is more or less cor- 



