~ PART III] THE MECHANISMS OF FLOWERS. 185 
various organs as follows: (1) The broad base of the vexillum, 
which is continuous with the superior and lateral portions 
of the tube, and even with part of its inferior aspect by means 
of an expansion (¢) just at the base of the free limb. (2) The 
base of the carina, which is attached to the inferior part of the 
edge of the tube in the interval left by the vexillum: though 
not half so broad as the base of the vexillum, it is broad and strong 
- enough to return quickly to its place after being bent downwards. 
| (3) The two al, whose flexible claws spring from the common 
' tube; the lamina of each bulges out at its base (g) more 
distinctly than in 7’. repens, to cover over the top of the staminal 
- column and help to keep it and the petals in their proper relative 
_ positions. (4) The ‘staminal tube, which is split superiorly to 
admit the free tenth stamen, and which divides in the hollow of 
the carina into stiff filaments which curve upwards and are slightly 
thickened at their ends. | 
; In the midst of the stamens lies the style, curving upwards till 
_ its stigma slightly overtops the anthers. 
If now a bee inserts its proboscis beneath the vexillum, while 
_ it clings with its forelegs on to the ale (which are coherent with the 
carina) resting its middle and hind legs on a lower part of the 
inflorescence, the carina and ale are drawn downwards, and the 
stigmas and anthers are thrust up against the under side of the 
_ bee’s head; the stigma, standing highest, receives the pollen 
_ brought by the bee, and instantly afterwards the anthers dust the 
bee with fresh pollen. Cross-fertilisation is thus insured ; self- 
fertilisation may take place as the bee draws back its head, but is 
__ probably neutralised and superseded by the immediately preceding 
 cross-fertilisation. 
_ Inorder to reach the honey in this way, an insect must possess 
_ a proboscis at least 9 to 10 mm. long. The pollen is accessible to 
all insects which can press down the carina; and it is clear that 
_bees when collecting pollen on the flower rericrn cross-fertilisation 
as well as when sucking honey. The red clover, like most flowers 
_ whose honey lies more than 7 to 9 mm. deep, is liable to the attacks 
of Bombus terrestris and other insects which use the holes that B. 
)  terrestrishas made. The small flowers of clover become conspicuous 
__ byaggregation into heads, and contain very abundant honey. 
A. Hymenoptera—A pide : (1) Bombus silvarum, L. 2 (proboscis 14mm.) ! 
(2) B. ian abc L. $2 (10—14)! (3) B. Rajellus, Ill. § § agape 
_ (4) B. agrorum, F. § 2 (10-—15)! (5) B. senilis, Sm. Q (14—15)! (6) B 
