ART IIL. | THE MECHANISMS OF FLOWERS. 97 
23. CoRYDALIS CAVA, Schweigg. and Kért. The flower is 
figured and described by Hildebrand (351, 358). 
In contrast to the pendulous flowers of Diclytra and Adlumia, 
which are symmetrical about two planes perpendicular to. one 
- another, and permit a double motion of the hood, to right and left, 
- we have in Corydalis cava horizontal flowers symmetrical about 
one perpendicular plane, and whose hood can only be thrust by 
insects in one direction, viz. downwards. The two outer petals, 
_ which are here superior and inferior, have ceased to be symmetrical, 
_ the upper one being produced into a long spur, curved downwards 
at the end, and reaching some 12 mm. backwards over the flower- 
stalk. In this spur is lodged a common prolongation of the upper 
_ stamens, which secretes honey and extends as far as the curved part 
of the spur. 
ec The two inner petals stand at the sides, and are fused with the 
upper petal at their bases; they are symmetrical, and unite at the 
apex to form a hood. A bee, to reach the honey stored at the end 
of the spur, must stand on the lower petal or on the hood, and 
thrust its proboscis between the hood and the upper petal; in 
doing this, it presses down the hood, and rubs the under surface 
of its head on the stigma, which, being placed on a stiff pistil, does 
not bend downwards, and has been covered with pollen before the 
opening of the flower. The hood, on withdrawal of the pressure, 
springs back into its former place, and covers the pistil and stamens 
as before. 
So, in young flowers, bees dust the lower part of their heads 
with pollen ; in older ones they supply the stigma with pollen from 
previously visited flowers. As the bees habitually go from below 
“upwards on each plant, they bring pollen to the lower and older 
flowers of one plant from the upper and younger flowers of 
another, and thus regularly induce crossing of separate stocks. 
This is very noteworthy, since Hildebrand has shown by many 
experiments that the flowers of C. cava are absolutely barren to 
their own pollen, very slight!y fertile to pollen from another flower 
of the same plant, and only thoroughly fertile when impregnated 
with pollen from a different plant. 
Since the spur of C. cava is 12 mm. long, and is at the very 
most filled with honey to the extent of 4 or 5 mm., it is quite 
impossible for the hive-bee with its proboscis of 6 mm. to reach 
_the honey in the legitimate way. Bombus terrestris, L. 2, might 
succeed better with its proboscis of 7 to 9 mm., occasionally even 
10 mm.; but even this species soon gives up thrusting its proboscis 
H 
