182 THE FERTILISATION OF FLOWERS. [parr ut. — 
by the bases of the cohering stamens, it surrounds the base of 
the ovary, and can only be reached through two apertures, one on 
either side of the base of the superior free stamen. An insect, 
to reach the honey, must thrust its head in beneath the vexillum, 
and must stand in doing this upon the two ale. In climbing 
on to the ale and thrusting its head below the vexillum, it forces 
up the latter and presses the ale and carina down; and the re- 
productive organs, protruding from the carina, are forced up against | 
the ventral surface of the insect. The organs all return to their | 
Fic. 59.—Trifolium repens, L. 
1.—F lower, from below. 
2.—Ditto, from above, after removal of calyx and vexillum. 
3. —Inner view of right ala. 
ce’, pouched swelling. 
former place when the insect leaves the flower; and cross-fertili- 
sation takes place regularly, since the stigma projects slightly 
beyond the anthers and therefore comes first in contact with the 
ventral surface of the insect. 
In addition to these characters, which Trifoliwm repens — 
possesses in common with many other Papilionaceous flowers, the _ 
following are peculiar to itself: (1) the arrangements for excluding 
certain short-lipped insects; (2) the conditions of rotation of the 
alse and carina; (3) the provisions for bringing back the parts of — 
the flower to their former place when pressure is removed. 
(1) The calyx-tube, which surrounds the claws of the petals 
and limits the movements of the vexillum and ale, is only 3 mm, 
