1915] SHERFF—BIDENS 305 
having achenes sometimes approaching those of Cosmos and with 
rays varying, in herbarium specimens, from yellow to white, rose, 
or violet (a single sheet frequently showing all these variations, as, 
for example, Palmer 674, Herb. Kew). 
During the past few years, certain writers, notably OLIVER 
and Hiern, S. L. Moors, and O. HorrMann, have described a con- 
siderable number of striking and positively new species of Coreopsis 
and Bidens from various parts of Africa. In their generic dis- 
tinctions, however, they have unfortunately been guided mainly 
by the direction of the barbs on the awns of the achenes, or, in cer- 
tain cases, they have had access at the time to immature achenes 
only. Regarding the latter point, the disadvantage and source 
of error are at once evident on examining the real distinctions be- 
tween Coreopsis and Bidens. As will be seen below, the presence 
of two more or less conspicuous lateral wings upon the achenes 
seems by far the most nearly constant character of Coreopsis as dis- 
tinguished from Bidens. But in several species of Coreopsis these 
wings are completely lacking on the immature achenes. Thus, 
species described from immature specimens as Bidens may later 
prove to be Coreopsis. Again, a species erroneously described from 
immature specimens as Coreopsis, because of a recognized resem- 
blance to some particular species of Coreopsis and disregarding the 
absence of wings, must thereafter be treated by botanists as Core- 
opsis until mature material can be obtained to prove its status as 
true Bidens. 
Concerning the direction of the barbs on the awns of the achenes, 
however, a more detailed statement is needed. Until compara- 
tively recent times, botanists referred to Bidens those species with 
retrorsely barbed awns, and to Coreopsis those species with an- 
trorsely barbed awns or with awns inconspicuous. But, from time 
to time in North America, new forms have been discovered, iden- 
tical in each case with a certain species of Coreopsis (as then de- 
limited) or Bidens except in the direction of the barbs on the awns. 
Asa Gray (cf, FERNALD, Rhodora 15:77. 1913), when confronted 
with such a form of “Coreopsis aristosa Michx.” (the then accepted 
name), designated it “C. aristosa in Bidentem transformata.” 
Later (Synop. Fl. N. Amer. 1%:294-296. 1884) he treated this 
