PS ee NY E MEI S 
DISK-COLORS 29 
forms, often amounting to a deep beautiful crimson. In others 
the disks are apt to turn a pale olivaceous color ; sometimes almost 
green, as in the green-disk form of A. divaricatus; and rarely to 
a full green. But while it is generally possible to say of a species 
that its disk is “usually crimson” (as A. rupicola) or “ usually 
red-sienna " (as A. biformis) or “usually olivaceous brown " (as 
A. sociatilis), it is not often that any species is wholly constant to 
its predominant color, nor is it easy to find any cause for the 
exceptions. For instance, side by side, in shade or in sun, the 
kindred of A. divaricatus, though seemingly the same in leaf and 
habit, may have disks turning crimson and others a pale olivaceous. 
The heads of a whole plant however are all alike in their disks. 
Color of pappus.—This is usually deepened in the herbarium, 
becoming somewhat ecru ; sometimes deeply so, as in A. patens ; 
among the Biotian species it is apt to become reddish, sometimes 
purplish or slaty. Species seem to differ considerably in the 
rapidity of this change, and in its first intensity ; and perhaps there 
may be a difference among individuals within the species. Young 
half-grown heads seem to deepen much more than those which 
had become a little expanded before collecting ; especially in A. 
nobilis and A. curvescens. In life the pappus is usually whitish, the 
same hue throughout a species from the beginning, bright in 4. 
subulatus, A. argillarius, etc., dingy in A. divaricatus, or even ecru 
in A. macrophyllus. In A. curvescens I have seen a faint trace of 
reddening already during life, and it becomes beautifully red in a 
few years inthe herbarium. In A. umbelliformis and A. Schreberi, 
I find it turning from ecru to a decided red in three years. The 
. more remarkably red examples (except the above) are old speci- 
mens which have been reddening in herbaria for forty to sixty 
years, and which caused much wonder among collectors at their 
inability to duplicate them in nature until it was perceived that 
aster-pappus is widely subject to change of color. 
Other asters of non-Biotian groups do not share this color- 
change so conspicuously. But it is not absent from them, various 
Calliastrum species reddening decidedly (as A. conspicuus); and 
A, patens becoming a dark ecru or a well-marked brown. 
Color of stem. — This is usually affected by sun or shade; the 
same stem may be reddened on the sunny side and greenish-brown 
