No. 423.] NORTHERN POLYPETALOUS FLOWERS. 229 
the large, black-dotted, bright-yellow flowers attract many flies, 
which feed on the pollen. The smaller-flowered species are 
rarely sought by insects, and self-fertilization is possible through- 
out the genus. The two small, reddish-flowered species belong 
to the genus Triadenum. The petals of 77zadenum virginicum 
are rose colored, with deeper veins, and do not exceed the calyx ; 
the honey glands are orange and the anthers bright yellow 
with white filaments. The flowers are very sparingly visited by 
insects, and after repeatedly watching them I have observed 
only two bees and three flies. The stem, the capsule, and often 
the leaves are a deep crimson, as is often the case in Hypericum. 
The change in the petals from yellow to red is probably corre- 
lated with the red coloration of the plant rather than due to 
insect selection. In Hypericum perforatum, which frequently 
has the foliage crimson colored, the yellow petals are tinged 
with rose in the bud, which fades away as the flower opens. In 
Epilobium palustre reddish flowers are more common when the 
stems afé red than when they are green. 
In the Cistacez, or rock-rose family, the genus Helianthemum 
(frostweed) has large yellow flowers, which throughout the day 
follow the sun. They are ephemeral, but the plants remain in 
blossom for a long time, as there is a succession of flowers, as 
in the crucifers. . There is no honey, but the pollen attracts a 
miscellaneous company of insects. As is frequently the case 
in pollen flowers, pollen falling from the anthers is not lost but 
lodges in the concave petals. The small greenish flowers of 
Lechea (pinweed) are self-fertilized. 
The violet family in the northern states contains 7 white, 
6 yellow, 4 purple, and 17 blue flowers. About 300 species of 
this family and 150 of the genus Viola have been described, 
Müller regards yellow as the original color of the violets, The 
small, short-spurred V. dzfora, which in the Alps is fertilized by 
flies, has yellow flowers; the large-flowered V. tricolor, variety 
alpestris, presents all stages in the passage from yellow to blue. 
« Many plants have flowers which are yellow throughout; in 
others the flowers are yellow when they open but change gradu- 
ally to blue ; and in others the change to blue occurs immediately 
after opening, or even before." V. calcarata, which has a spur 
