1879. | The Fertilization of Clitoria and Centrosema. 691 
line, this petal has a guiding groove (g) of considerable depth, 
which connects with a slight cup (7) at the very base, this cup 
serving as a receptacle for nectar. On its lower surface, just in 
front of this receptacle, the vexillum is provided with a solid spur 
(sf, Fig. vir), which forms one character by which this genus is 
distinguished from Clitoria, but which seems to perform no func- 
tion now. On the upper surface of the standard a white line, bor- 
dered on each side by fine lines of dark purple, runs from the 
basal guiding groove nearly to the apex of the petal, while others 
radiate from it on either hand, following the general direction of 
the veins of the standard. These marks, like those of the gpecies 
last discussed, serve as guides to the nectar, which is poured into 
its receptacle, from a vaguely nine to ten-lobed annular gland, 
through the split in the staminal tube. The wings are coherent 
with the keel, are laterally inflated, and are so arranged as to pre- 
vent anything larger than the proboscis of a butterfly from reach- 
ing the nectar of the flower excepting by way of the guiding 
groove. The keel petals. are grown together along both edges 
with the exception of a small space at their base and another at 
their apex. On the border next the vexillum, at about one-third 
the distance from its base to its apex, each keel-petal bulges out- 
ward to form an egg-shaped, thin-walled protuberance (Fig. vill, 
u), the two being approximated on the median line. Half way 
between this and the tip, another common inflation (v) forms a 
closed pouch in which the stigma and anthers commonly lie, the 
style and stamens being strongly curved. 
In reaching its head under the keel for the purpose of pro- 
truding its tongue into the nectar receptacle, through the guiding 
groove, a bee encounters the first-mentioned protrusion, which, 
with the inflated sides of the keel and the wings, acts as a spring, 
keeping the keel in its normal position, with the stigma and 
anthers concealed within it, in their pouch. But when this pro- 
truding pouch is pressed from below it bends the keel on its 
back and forces it slightly backward at its base, so that the stigma 
‘and anthers—which move but little—are protruded from the split 
apex of the keel and come in contact with the back of the bee. 
After the pressure is removed the elasticity of the parts returns 
them to their former position. 
In spite of the guiding marks some insects fail to find the nec- 
tar. For example, one day in August an ichneumon-fly was seen 
