No. 423] NORTHERN POLYPETALOUS FLOWERS. 213 
The blue flowers of Arabis cærulea are likewise sought by flies, 
while the nocturnal flowers of Hesperis tristis are dark-colored 
and dependent upon their fragrance. The parti-colored appear- 
ance of the flower clusters and the changes of color of individual 
flowers would indicate that the guests were a miscellaneous group 
of insects, with the color sense but feebly developed. How 
comparatively unimportant the color of a flower may become is 
well illustrated by Lepidium sativum. The small white flowers 
can be seen only a short distance, and in rainy weather do not 
expand. Yet they possess a strong scent, and Miiller found 
them visited more frequently by insects than any other crucifer. 
Throughout the species of this family the petals have not been 
extensively modified either in form or color. 
The flowers of the Capparidaceze resemble those of the 
Cruciferze both in form and color. Polanisia graveolens (clammy 
weed) has purplish sepals and stamens, and whitish petals. 
There are three species of mignonette (Resedacez) in the 
northern states. The flowers are especially attractive to small 
bees of the genus Prosopis. These bees, which have an aro- 
matic odor, are coal black, marked with yellow. They are 
doubtless attracted by the sweet fragrance, which can be per- 
ceived at a long distance. Reseda luteola (yellow weed) has 
greenish-yellow flowers and is cultivated for its yellow dye. 
R. alba has white flowers. In R. odorata the receptacle is at 
first yellow, changing to orange red ; the petals are white or red, 
and the anthers red. The perfume is intense. On flowers 
growing in his window Müller collected five species of Prosopis, 
besides other insects. The strong scent of these flowers probably 
compensates for their small size and greenish colors. 
The Sarraceniales contain two remarkable carnivorous families, 
the Sarraceniacez, or pitcher-plants, and the Droseracez, or 
sundews. The leaves, which are. adapted to trap insects, are 
more conspicuous than the flowers. Sarracenia purpurea has 
purple-veined leaves and large purple flowers, while S. fava has 
green leaves and yellow flowers. The walls. of the orifice, and 
the hoods, or lids, of the pitchers are the most highly colored 
parts. Leaves without ascidia or pitchers are green, The 
upper part of the pitcher of .S, laciniata. is pure white, marked 
