688 The Fertilization of Clitoria and Centrosema. [ November, 
THE FERTILIZATION OF OUR NATIVE SPECIES OF 
CLITORIA AND CENTROSEMA. 
BY WILLIAM TRELEASE, 
VISITOR to the Southern States in the early summer will 
notice among the most conspicuous flowers of dry, open 
wood-borders and fields, the two related leguminous species 
known to botanists as Ciitorta mariana and Centrosema virginiana; 
the former a low vine, sometimes twining for a few feet up some 
supporting shrub; the latter a strong, slender twiner, not infre- 
quently ascending to the height of ten or more feet. In accord- 
ance with its small size, the former has, as a rule, but one or two 
flowers expanded at a time, and they are of a pale purple, so that 
it is far outshone by its relative, whose entire length is often cov- 
ered by bright purple flowers—not quite so large, to be sure, as 
those of Clitoria, but compensating for diminished size by 
increased number and depth of color—hence a shrub covered by 
this vine in full bloom is often an object of great beauty. 
If we examine a flower of either species we find that its vex- 
illum or standard (s, Fig. 1) is the lowest petal, while in most 
leguminous plants it is the uppermost when the flower is in the 
position which it naturally occupies on the plant; and this posi- 
tion allows it to serve in the species under consideration as an 
alighting place for insects. 
An examination of the flower of Clitoria will show that the 
lateral borders of the horizontal standard are folded upwards to 
form a trough, this structure forcing insects to enter the flower 
on the median line and leading them directly beneath the keel 
(4). The uniform pale-purple color of the rest of the corolla is 
deviated from in this trough by the production of special guiding 
marks, which combine with the curvature of the standard to lead 
all insects into the flower in a constant direction. These marks 
consist of a yellowish spot near the apex of the standard, which 
narrows into a line following the middle line of the petal. From 
the base of this line radiate dark-purple lines on each side, their 
widest divergence being just below the widest part of the yellow 
line. The wing petals (w) are coherent with the keel at the point 
p, and beyond this point they diverge somewhat, thus aiding ina 
: _ slight degree the upturned borders of the standard. The keel is . 
2 split on its lower border, but when undisturbed the edges are 
