160 



GENUS CHRYSOTHAMNUS. 



another section and universally admitted as a Chrysothamnus, has resin-dots almost as 

 prominent as those of the Punctati (compare enlarged leaves of plates 24 and 28, and 

 fig. 24). 



A different point of contact between the two genera under consideration was sug- 

 gested by Gray (Proc. Am. Acad. 8:641, 1873) and the suggestion was followed up by 

 Greene (Erythea 3:114, 1895). According to these authorities, there is scarcely any 

 difference between Chrysothavinus bolanderi and Haplopappus discoideus. It must be 

 admitted that the superficial similarity is very marked and that the peculiar dense 

 tomentum of the twigs is suggestive of a genetic affinity. But the heads of the former 

 are much narrower than those of the latter, the involucre is decidedly narrowed at the 

 base, and the bracts are carinate and positively arranged in vertical rows, although 

 these rows are somewhat obscure. In the Haplopappus the bracts are much more folia- 

 ceous, flatter, wider, more loosely arranged, not carinate, and with not even a suggestion 



Fig. 24. — Leaves of Chrysothamnus teretifolius and C. albidus, to illustrate resin pits: a, C. teretifolius; b, C. albidus. 



Both X 50. 



of a vertical arrangement. It seems that here again we have, not a case of close phylo- 

 genetic relationship, but rather one of superficial resemblance between plastic groups 

 that have come under the same environmental influence. It seems quite likely that 

 the two botanists whose opinion has just been stated, were misled through errors in 

 identification. At the National Herbarium, where Greene did his work, there are only 

 three sheets labeled C. bolanderi and two of these are plainly Haplopappus discoideus. 

 The same error occurs in the Greene Herbarium and certain early determinations at the 

 Gray Herbarium were similarly erroneous. 



Chrysothamnus is thus seen to be a fairly homogeneous assemblage of species; to be 

 most closely related to Haplopappus section Ericameria (or possibly section Macro- 

 nema); and to bear a less direct relation to Chondrophora, this latter consisting of the 

 typical species of De Candolle's Bigelovia. 



DIVISION INTO SECTIONS. 



The first attempt at an arrangement of the species into natural sections was by Gray 

 in 1873 (Proc. Am. Acad. 8:638). This was under the generic name of Bigelovia, which 

 was then so extended as to include many species since referred elsewhere. Those be- 

 longing to what now constitutes the genus Chrysothamnus were embraced in two sections, 

 namely, Chrysothamnopsis, including three species, all of which now form part of C. 

 parryi, and Chrysothamnus, composed of 8 species belonging to the sections Punctati, 

 Typici, Pulchelli, and Nauseosi of the present treatise. The primary division under 

 this second section was based chiefly upon the pubescence of the achenes, a character 



