178 THE FERTILISATION OF FLOWERS. [PART III, 
flowers which wither unexploded when insects are excluded produce 
seed by self-fertilisation. 
In spite of their very accurate mechanism, I have observed by 
watching insect-visitors that the flowers have two imperfections. 
In the first place they continue to secrete honey after explosion, 
and in the second, the young unexploded flowers very frequently 
permit insects to obtain the honey without performing any service 
in return. 
It is plain that the continued secretion of honey after explo- 
sion is detrimental to the plant; for it leads the insects to visit 
exploded flowers instead of restricting their visits to flowers that re- 
quire their aid. I have seen hundreds of hive-bees sucking honey 
on exploded flowers, thrusting the proboscis laterally over one of 
the alz, and not coming in contact at all withthe stigma or anthers, 
which were pressed close up against the vexillum. 
The other imperfection is also taken advantage of by the 
hive-bee, as Henslow has remarked. The bee probably finds it — 
unpleasant to have its proboscis struck by the exploding column 
at each visit; for it prefers, even in the case of young flowers, to 
insert its proboscis laterally close to one of the alz,so that no 
explosion results. Although bive-bees are by far the most 
numerous visitors of this flower, I have never seen them effect 
explosion ; but I have often observed them from a short distance 
acting in the manner just described. Though I have frequently 
watched this plant, I have never succeeded in seeing explosion 
actually performed, though the number of exploded flowers that 
we meet with shows that it must take place very frequently. 
Butterflies visit the flowers in great numbers, and it is doubtless 
by them that explosion and cross-fertilisation are effected; but they — 
are generally too wild to permit close observation of their move- 
ments. Once I had a good view of Hesperia thawmas, Hufn., suck- 
ing a young unexploded flower, but like the bees it inserted its 
proboscis from the side and did not cause explosion. A fine needle 
inserted in the middle line of the flower causes explosion, and the 
thin proboscis of a butterfly is undoubtedly sufficient to do the same. 
A. Hymenoptera—A pide : (1) Apis mellifica, L. %, s. very freq. ; (2) | 
Megachile pyrina, Lep., s. B. Lepidoptera—(a) Rhopalocera: (3) Pieris 
brassice, L.; (4) P. rape, L.; (5) P. napi, L., all three ab. ; (6) Vanessa 
urtice, L.; (7) Colias hyale, L.; (8) Satyrus hyperanthus, L. ; (9) Tuyceena 
argiolus, L. ; (10) Hesperia thaumas, Hufn. ; (6) Noctue : (11) Plusia gamma, L. 
Fifteen additionsl visitors (eleven Apidae, three Lepidoptera, and Bembex 
rostratus) are recorded in No, 590, 11. 
