496 THE AMERICAN NATURALIST. [VoL. XXXIII. 
the three outer green on the lower side; in Nymphea advena 
the lower. half of the outer sepals is green, and the upper half 
yellow; Trollius laxus, which grows in dense swamps, has 
greenish-yellow sepals, but the culture varieties are bright yel- 
low, while the perianth of Veratrum viride is yellowish-green. 
Henslow thinks it probable that the yellow coloration of the 
petaloid structures is correlated with the yellow coloring of the 
anthers and pollens, universal among gymnosperms and very 
prevalent among angiosperms, and also extending to the anther 
scale of Pinus and the sporophylls of Lycopodium. Certainly 
yellow is the first color to be developed in many dicotyledonous 
families. 
The 12 species of the Commelinaceæ all have blue flowers, 
except Tradescantia rosea, which is rose-colored, and the small- 
est northern species with narrow grass-like leaves and few flow- 
ers. Blue in this family appears to have been preceded by a 
reddish stage, and this view is strengthened when we remem- 
ber that many blue Boraginaceæ have passed through a red 
stage, as Myosotis, Pulmonaria, and Echium, several species 
changing from red to blue during the course of individual 
development. The filaments of Tradescantia are bearded as 
in Verbascum, which is visited by pollen-collecting bees. 
The original color of the Pontederiaceæ was almost certainly 
yellow, as it still is of the smallest species, Heteranthera dubia, 
water star grass, which has a slender stem and linear, sessile 
leaves. Every stage of the transition from yellow to blue is 
shown by_ Viola tricolor, and in Gentiana the simplest species, 
G. lutea, is yellow, but the more highly specialized species are 
purple-blue. The middle lobe of the upper lip of Pontederia 
cordata is marked by two yellow spots, which serve as honey 
guides. This is one of the handsomest as well as commonest 
of river plants, producing thousands of spikes of purple-blue 
flowers with blue anthers. The most important visitors are 
Bombus vagans and B. borealis, though I have also collected 
upon the flowers two other k four Lepidoptera, and four’. 
Diptera. 
The Juncaceæ have a small, oul six-parted perianth which 
is often reddish or purplish brown. The flowers are anemo- 
