play, and the tinge of blue was so faint that it could hardly have served as a guide. (11/8.  A fact mentioned by Hermann Muller ‘Die Befruchtung’ etc. page 347, shows that bees possess acute powers of vision and discrimination; for those engaged in collecting pollen from Primula elatior invariably passed by the flowers of the long-styled form, in which the anthers are seated low down in the tubular corolla.  Yet the difference in aspect between the long-styled and short-styled forms is extremely slight.)

The conspicuousness of the corolla does not suffice to induce repeated visits from insects, unless nectar is at the same time secreted, together perhaps with some odour emitted.  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.

It would appear that either the taste or the odour of the nectar of certain flowers is unattractive to hive or to humble-bees, or to both; for there seems no other reason why certain open flowers which secrete nectar are not visited by them.  The small quantity of nectar secreted by some of these flowers can hardly be the cause of their neglect, as hive-bees search eagerly for the minute drops on the glands on the leaves of the Prunus laurocerasus.  Even the bees from different hives sometimes visit different kinds of flowers, as is said to be the case by Mr. Grant with respect to the Polyanthus and Viola tricolor.