parr] = THE MECHANISMS OF FLOWERS. 197 
against its back, it stays for some seconds motionless as though 
stunned, and then turns round, freeing .itself from the style, 
and begins to gather pollen upon the anthers with its mouth 
and legs. 
The behaviour of humble-bees is on the whole similar to that 
of the hive-bee. But while the hive-bee is only strong enough 
_ to cause the flower to explode, often causing only the shorter 
stamens to escape, humble-bees are able easily to force open any 
_ flower in which the vexillum has become erect; and they may be 
seen not unfrequently to break open, though with considerable 
effort, flowers in which the alz are still inclosed by the vexillum, 
Cross-fertilisation is insured, since the stigma is always mature 
in flowers capable of exploding, and since the bee’s back is always 
touched by the stigma an instant before the fresh pollen is applied 
- to it. And even the flower to which the bee pays its first 
_ visit, and whose stigma is not pollinated in the first instance, has 
a fair chance of being fertilised subsequently, as the style curls 
round so far as to bring the stigma again uppermost. A second 
visitor can therefore easily apply pollen to it from the same or from 
another flower, and the flower is certain to be again visited. I 
have only occasionally seen hive-bees and humble-bees visit 
exploded flowers, but the pollen that they leave is gleaned by the 
"smaller bees, flies, and beetles, which are not strong enough to 
force open the young flowers. I have found females of Andrena 
_fulvicrus, K., Halictus zonulus, Sm., and Osmia fusca, Chr., busily 
collecting pollen on exploded flowers; Rhingia rostrata and the 
beetles Meligethes and Anthobium are often to be seen feeding on 
these remnants of pollen. There is no doubt that many flowers 
of Sarothamnus, which have been exploded by bees not yet dusted 
_ with pollen, are fertilised by such supplementary visitors. The 
shorter stamens which apply their pollen to the under sides of bees 
or of Rhingia, and the position of the stigma after explosion when 
it also is liable to come in contact with the under surfaces of 
insects, stand in close relation with this supplementary process of 
fertilisation. 
In the Broom as in Laburnum, the vexillum is marked in its 
| lower part by dark lines coursing towards the base of the flower. 
If the flower contained honey, these lines could only be explained 
as pathfinders, but here the’ flowers have neither any free honey 
/ nor a nectariferous swelling such as exists in and round the in- 
 sertion of the vexillum in Laburnum. In this case the dark lines 
_ may either be a useless inheritance from ancestors whose flowers 
