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Show 422 HABITS OF INSECTS CHAP. XI. men1ory of former visits could. have c~me into play, and the tinge of blue was so faint that It could hardly have served as a gui'd e . * 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 1nany times daily a wall covered with Linaria cyrnba Zaria in full flower, and never saw a bee even looking at one. There was then a very hot day, and suddenly Inany 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 er1'nus 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 Pedieularis sylvatica, Polygala vulgaris, Viola tricolor, and some species of Trifolium, I have watched the flowers day after day without s~eing 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 * A fact mentioned by H. Muller ('Die Befruchtung,' &c., p. 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 anther:; are seated low down in the tubular corolla. Yet the difference in aspect between the long-styled and . short-styled forms is extremely shght. CHAP. XL IN RELATION TO CROSS-FERTILISATION. 423 labour of other species. Mmnory al . .i! 1 so comes 1n to play lOr, as a ready remarked bees k th . . ' h 1 ' now e pos1t1on of eac c ump of flowers in a garden I h h . · ave repeatedly seen· t h em p· assing round a corner' but ot ·h e r. W I. s o 1. n ~ as straig t a hne as possible from one plant ofF . ll d f L . . ' raxino a an o Inana to another and distant o f th • • <- ne o e samo 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-b~es, or to both; for there seems no other reason w.h! certain open flowers which secrete nectar are not VISited by them. The small quantity of nectar secreted bhy s· ome of these flowers can hardly be the cause of ' t eu neglect, as hive-bees search eagerly for the minut drops on the glands on the leaves of the Prunus lauroc~ r~sus: Even the bees from different hives someti1nes VISit different kinds of flowers, as is said to be the case ~~Mr. ?rant with respect to the Polyanthus and Viola trwolor. I have known humble-bees to visit the flowers of Lo.belia fulgens in one garden and not in another at ~he distance of only a few miles. The cupful of nectar In th~ labellum of Epipactis latijolia is never touched by. hive- or humble-bees, although I have seen them ~y1ng close by j and. yet the nectar has a pleasant taste to us, and Is hab1tually consumed by the common w~sp. As far as I have seen, wasps seek for nectar in this countr.Y only from the flowers of this Epipactis, Sc~ophular~a aquatic a, Symphoricarpus racemosa, t and Tntoma ; the two former plants being endemic, and the two latter exotic. As wasps are so fond of sugar * 'Gard. Chron.' 1844-, p. 374. t The same fact apparently hoJds good in Italy, for Delpino l:!ays tllut the flowers of these three plants are alone visited by wasps : • N ettarii E~tranuziali, Bullettino Entomologico,' anno vi. |