230 THE AMERICAN NATURALIST. [VoL. XXXVI. 
from 13 to 25 mm. in length and is fertilized by Lepidoptera, 
chiefly by Macroglossa stellatarum, displays, according to Kerner, 
in the meadows of the western Alps a blue corolla, and a yel- 
low corolla in the eastern Alps. Darwin transplanted a large, 
uniformly colored, dark-purple variety of the pansy while in full 
flower, and it subsequently. produced smaller flowers, with the 
lower petals yellow. The white forms appear to be derived from 
blue progenitors, for the former are purple veined and may be 
tinged with violet. Blue species of Vjola which often have 
white flowers are V. palmata, V. obliqua, and V. odorata, and 
in various stages V. canadensis. Pathfinders among white 
northern polypetalous flowers are of infrequent occurrence. 
The most prominent instances are Saxifraga michauxii, with 
three of the unequal white petals marked with yellow ; Oxa/zs 
acetosella, white with reddish veins; Parnassia, with greenish 
veins ; Magnolia macrophylla, ZEsculus hippocastanum, Lespedeza 
hirta, and L. capitata display purple spots. In the white violets 
the purple honey guides are highly developed, which may be 
best explained by supposing them descended from blue-flowered 
ancestors with darker veins similar to existing species. 
The beautiful and richly variegated varieties of V. tricolor, the 
garden pansy, are due partly to selection and partly to hybridi- 
zation. The corolla may be pure white, yellow, red, blue, 
purple, or black; or there may be combinations of yellow and 
blue; yellow and red; yellow, blue, and white; and blue and 
white. According to Strasburger, in the pansy the cells of 
the epidermis of the petals contain both violet sap and yellow 
granules. “The striking diversities in color presented by dif- 
ferent parts of a given petal depend wholly upon combinations 
of these two elements of color, — namely, violet sap and yellow 
granules."! Places which are devoid of both these elements are 
white, as the light is refracted and reflected by the intercellular 
spaces containing air. When sections of white roots of a violet 
plant are exposed to the air they change to violet ; and the leaves 
of V. cucullata when grown at alpine altitudes become yellow. 
While the violets vie with the roses in popular favor, they do 
not prove attractive im an equal degree to insects. In MaineI © 
1 Goodale. ee NE i 
