I watched for a fortnight many
times daily a wall covered with Linaria cymbalaria in full flower, and
never saw a bee even looking at one. There was then a very hot day, and
suddenly many bees were industriously at work on the flowers. It appears
that a certain degree of heat is necessary for the secretion of nectar;
for I observed with Lobelia erinus that if the sun ceased to shine for
only half an hour, the visits of the bees slackened and soon ceased. An
analogous fact with respect to the sweet excretion from the stipules of
Vicia sativa has been already given. As in the case of the Linaria, so
with Pedicularis sylvatica, Polygala vulgaris, Viola tricolor, and some
species of Trifolium, I have watched the flowers day after day without
seeing a bee at work, and then suddenly all the flowers were visited by
many bees. Now how did so many bees discover at once that the flowers
were secreting nectar? I presume that it must have been by their odour;
and that as soon as a few bees began to suck the flowers, others of the
same and of different kinds observed the fact and profited by it. We
shall presently see, when we treat of the perforation of the corolla,
that bees are fully capable of profiting by the labour of other species.
Memory also comes into play, for, as already remarked, bees know the
position of each clump of flowers in a garden. I have repeatedly seen
them passing round a corner, but otherwise in as straight a line as
possible, from one plant of Fraxinella and of Linaria to another and
distant one of the same species; although, owing to the intervention of
other plants, the two were not in sight of each other.
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