parti.) | THE MECHANISMS OF FLOWERS. 203 
carina. In the middle of its upper border, each ala has a small but 
deep fold (a, 2, 4), which fits into a concavity in the upper surface 
_ of the carina (a’, 3) immediately behind the swelling which contains 
F the pollen. Close behind this the side of each ala bulges inwards, 
_ forming a depression, much broader and not less deep, which unites 
‘so firmly with a broad but shallow concavity in the upper surface of 
the carina ()’, 3) that it requires the greatest care to separate the 
two without tearing. This intimate union is due to the fact that 
the epidermis of the two petals over part of the surfaces of contact 
is composed of large hexagonal cells (,'; to ;4y mm. in diameter) of 
which those on the one petal are strongly convex, and fit into cor- 
responding concavities in the cells on the other. Thesame kind of 
_ union thus connects individual cells as on a larger scale connects the 
two petals. 
The ale and carina return after each depression to their former 
_ place. This is due: (1) to their own elasticity ; (2) to the processes 
 (¢, 2, 4) which pass backwards and inwards from the superior basal 
angles of the ale to lie upon the staminal column ; (3) to the two 
superior basal lobes of the carina (g, g, 2, 3), which embrace the 
 staminal column, and leave only a narrow slit between them in the 
middle line; (4) to the broad base of the vexillum, which curves 
round on each side so as to embrace completely the claws of the 
ale and carina, while it in turn is embraced and held firmly in 
position by the calyx. By these four conditions all the parts of the 
flower are caused to return accurately to their former places after 
each insect-visit. The flowers therefore preserve the same appear- 
ance, and are visited repeatedly by insects, so that their pollen is 
zarried away bit by bit, and the stigma at length rubbing on the 
} ‘under side of the insect becomes -vincid (cf. Lathyrus pratensis) 
and covered with pollen brought from other flowers. 
Though the parts of the flower close up firmly, their small size 
akes it easy for most bees to reach the honey. The abundance of 
honey and the aggregation of the flowers in handsome racemes 
lead to plentiful insect-visits. 
| A. Hymenoptera—(a) Apide : (1) Apis mellifica, L. 8 , exceedingly abundant. 
(It passes up the racemes, sucking for two to three seconds on each flower. When 
| collecting pollen, it thrusts its head farther into the flower to depress the 
' carina as much as possible ; it takes at least six to eight seconds to brush off 
the pollen) ; (2) Bombus agrorum, F. 9 &; (8) B. Berne L. $; (4) B 
R ajellus, Ill. §; (5) B. Scrimshiranus, K. ¢ 2 %; (6) B. (Apathus) vestalis, 
Foure. ¢; (7) Eucera longicornis, L. ? ) al only sucking: Various species 
vith abdominal collecting-brushes, viz.: (8) Megachile versicolor, Sm. 9; (9) | 
y circumeincta, K. 9, ab. ; (10) M. aiimaet. K .%;(11) M. Willughbiella, 
