220 THE FERTILISATION OF FLOWERS. [PART III. 
Though almost exclusively adapted for fertilisation by bees, 
many Papilionacez allow their honey to be ‘stolen by Lepidoptera 
and long-tongued flies (e.g. Onobrychis, Lotus, Medicago falcata). 
In others (e.g. Vicia sepium) the petals close up so firmly that only 
those bees which are in the habit of burrowing with all their 
strength, can force an entrance. Such forms as these exclude all 
visitors which would rob the flower of its honey without giving 
any return; but this advantage is more or less cancelled by the 
great diminution in the number of serviceable visitors. 
Trifolium pratense excludes short-lipped bees from its honey 
by adhesion of the nine coherent filaments with the claws of the 
petals to form a long tube; the same end is attained in Vicia faba : 
by the length of the claws of the petals and of the calyx-tube. — 
Both plants are the more visited on this account by the hard- 
working humble-bees ; but on the other hand they are liable to be 
often plundered by robber-bees which bite through the tube. 
The great variety of arrangements in the various Papilionacez 
seems to be partly due to the manner in which every advantageous ~ 
modification brings some disadvantage in its_.train ; for in this way 
it is possible to have various combinations existing together, all — 
perfectly adapted to the given conditions of life 
CHSALPINIACEZ AND MIMOSACE. 
In these two families the essential organs are freély exposed. — 
The petals or the stamens, or both together, attract insects. In 
Mimosacee the flowers are regular and united in capitula. In — 
Acacia Julibrizzin the central flower of the capitulum is trans- 
formed into a great nectary. In Amherstia nobilis the carina is— 
abortive, and the alz assume the function of rendering the flower 
conspicuous ; the honey-receptacle is hollowed out into a long tube, 
which, together with the brilliant colour of the flowers, suggests 
humming-birds as the fertilisers (178, 360). 
Fritz Miiller found Cassia multijuga (Cosalpiniacee) abundantly : 
visited by bees (Xylocopa, Centris) in South Brazil. The pedicles 
were covered with larvae of Membracide, which secreted drops of — 
honey at the posterior end of the abdomen, and this honey was 
sought by 7'rigonia cacafogo (590, III.). 
Cassia (?) is visited by humming-birds (J/imus) in Chili (Darwin, 
No. 164). 
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