1907]  Bartlett,— Flower Color of the American Diervillas 147 
FLOWER COLOR or THE AMERICAN DrERvILLAS.— The change in 
flower color which follows pollination in the Asiatic species of Dier- 
villa § Weigela is often cited as a striking case of adaptation to pol- 
lination by bees. In all but one of the Weigelas the flowers are at 
first white or merely roseate-tinged, but after pollination they change 
quickly to deep rose or carmine, in which condition they remain 
fresh for some length of time, serving to attract bees to the shrub. 
Only the white flowers are visited for honey, however. Among the 
American species of Diervilla, which belong to a section of the genus 
distinguished from $ Weigela by the smaller yellow flowers, the 
corresponding phenomenon seems to have been recorded only by 
Mrs. Dana. In “How to know the Wild Flowers" she says of Dier- 
villa Lonicera Mill. (D. trifida Moench): “The lower lobe of the 
corolla is crested and more deeply colored than the others, thus advis- 
ing the bee of secreted treasure. .... When the blossom has been 
despoiled and at the same time fertilized, for the nectar-seeking bee 
has probably deposited some pollen upon its pistil, the color of the 
corolla changes from a pale to a deep yellow...." Other observers 
have noticed that the flower of this species is not always “light yel- 
low” or “honey yellow," but have apparently ascribed the differences 
to specific variability. 
In shady woods the change in Diervilla Lonicera is not very notice- 
able, but in dry localities where the growth of the shrub is stunted, 
as for example on Mt. Chocorua, N. H., and on the summit of Great 
Blue Hill, near Boston, the flowers become deep scarlet. The lip is 
the first part to show signs of change and it remains always of a deeper 
hue than the rest of the corolla, becoming, on Blue Hill, almost 
maroon. At the Arnold Arboretum, where all the American Dier- 
villas are cultivated under moderate conditions of shade and moisture, 
fresh flowers were compared with Ridgway’s standard color scale and 
the following changes noted. In D. Lonicera Mill. the corolla is at 
first citron yellow. The lip changes to poppy red and the other lobes 
to scarlet. In D. rivularis Gattinger the change is from yellow to a 
lightly suffused, dull poppy red, most intense on the lip. In D. 
sessilifolia Buckley the citron yellow corolla changes to cadmium 
yellow except on the lip, which becomes orange. D. splendens 
Carriére, which Mr. Rehder is inclined to consider a hybrid between 
D. Lonicera and D. sessilifolia, changes from canary yellow to pale 
orange, with an orange lip. In this character, as well as in its time 
