PART III. | THE MECHANISMS OF FLOWERS. 213 
is curved more inwards, and the swollen ends of the filaments move 
with friction in the cone. On this account the union of the 
two carinal petals is strengthened by a still more marked out- 
growth (b, 1, 4), and the ale and carina are connected with each 
other and with the staminal column still moré firmly. Each ala 
has at the base of its limb, close below its upper margin, a 
‘depression or invagination pointing forwards and downwards 
 (¢, 2, 5, 6), which is very firmly attached to a corresponding 
depression on the upper surface of the carinal petal (¢, 1, 4); 
not only are the two pouches closely applied to one another 
_ throughout their whole extent, but over a great part of the surfaces 
in contact large hexagonal cells of the one petal project into hollows 
_ in corresponding cells on the other, so that it is scarcely possible 
to separate the petals from one another without tearing. More- 
_ over, the anterior part of the ala is kept in a definite position 
relatively to the carina by a fold or groove (d’, 2,5) in its upper 
margin which fits into that groove (d) upon the carina which 
- separates the pouch (a) from the edge. This second union of alz 
and carina is strengthened by two deep and narrow depressions of 
the vexillum, which appear on its under side as hard, sharp ridges, 
converging anteriorly (d’, 1, 3), and are received into the anterior 
alar grooves (d’). 
The position of the alz and carina relatively to the staminal 
column is maintained very firmly and accurately. Each carinal 
} pe etal possesses a lobe at its base (e, 4, 5), directed upwards and 
pawards, which lies upon the upper surface of the column and 
extends almost to the middle line. These two carinal lobes which 
Biibtace the column are pressed down and kept in their place by 
two processes of the ale (e¢’, 5, 6), directed inwards and backwards ; 
the alar processes are themselves made secure by the Neate: 
_ on whose broad, strong base two rounded swellings occur (0’, 3) 
which rest upon two narrow surfaces of the ale (0d, 5, 6) passing 
horizontally backwards from the alar processes (e’). 
_ This firm union of the parts of the flower is of service to the 
plant in three ways. In the first place, it obliges an insect in 
| search of honey, when standing on the alee and thrusting its head 
_ beneath the vexillum, to use so much force in separating the ale 
and vexillum that the brush and piston mechanism is set in action. 
Se ondly, it ensures the perfect return of all the parts to their 
| original position when the pressure is removed, and sa_causes the 
IP flower to retain its youthful appearance and to receive the repeated 
visits that its whole construction is designed for. Thirdly, it 
