No. 411.] NORTHERN APETALOUS FLOWERS. 205 
of Aristolochia, which was first studied by Sprengel, ‘was 
long," says Müller, “ the only example known of a temporary 
prison for insects." Progressive steps toward this structure 
are presented by Asarum and Heterotropa. The flowers of 
Aristolochia are lurid purple, with a yellowish-green tube; the 
tube of Asarum is greenish or brown-purple, puberulent with 
purple hairs; or in A. macranthum the tube is mottled with 
violet within. According to Kerner, South American species 
of Aristolochia are of immense size and are used as caps by 
children at play; in color they are a combination of cream and 
deep maroon purple. Purplish coloring of bracts and sepals is 
of so common occurrence, even extending to the whole plant, 
that in this family it has doubtless been developed directly 
from the primitive green without passing through any inter- 
mediate stage. The flowers should be compared with the 
pitcher-like leaves of Sarracenia and the spathes of Arum, as 
all three serve as traps for small flies and are lurid purple, a 
color probably attractive to these insects. Rudimentary petals - 
occur in Asarum canadense. 
The flowers of the Polygonacez, or buckwheat family, are 
devoid of petals and are wind-fertilized, as in Rumex, or au- 
togamous or entomophilous, as in Polygonum. In the genus 
Eriogonum, growing west of the Mississippi, the campanulate 
calyx is usually yellowish or white, sometimes changing to 
pink. The calyx of Rumex (sorrel) is small and commonly 
green, but in R. venosus it is red, and the fertile panicles of 
R. acetosella turn reddish; but the achenes, or fruit, are usu- 
ally red, and frequently the stems and leaves, as in A. san- 
guinea. Red butterflies, which are attracted by red coloration, 
were often seen by Miiller in the Alps seated upon the plants 
when in seed, and a species of Halictus was observed fre- 
quently collecting pollen. The plants of the Polygonacec 
tend to develop red rather than yellow coloration; but in 
Rumex persicarioides (golden dock) the fruiting calyx becomes 
orange-colored, and the roots of several species of dock are 
yellow. 
Of the thirty-eight species of the genus Polygonum (knot- 
weed) ten are white, ten red, three purple, and fifteen green. 
