As the quantity of nectar of a given species of plant becomes smaller, irrespective of its sugar con- centration, so the number of bees working that species of plant becomes reduced. This is not due to old bees that have been working this crop for some time deserting it in favour of a more profitable crop, but to the natural death of these old bees and the fact that their places are not taken by new bees. Young foragers are not attracted to the crop concerned because its presence is not communicated to them by the old bees still working upon it. The range of nectar concentration (% total carbohydrate) in the flowers of many species of plants growing in a given district varies from day to day and even from hour to hour. Such changes are almost certainly directly due to changes in the atmospheric humidity. The changes are greatest in flowers, such as hawthorn, with relatively unprotected nectaries. 3. Honeybees respond to the concentration of nectar secreted by the flowers of plants, working in the greatest numbers on those plants with the highest nectar concentration. 4. When two or more species of ' bee-plants' are in flower simultaneously the species which will attract most honeybees will be that in the flowers of which the nectar is most highly concentrated. This accounts for the occasional failure of honeybees to work the flowers of fruit trees when other flowei^^p available to them. 5. Both nectar abundance and nectar concentra- tion appear to have considerable effect upon honeybee activity. From the data at present available it appears correct to conclude tentatively that nectar concentra- tion decides in the first instance which species of plant will be visited in preference to others in flower at the same time, and that nectar abundance then determines the proportion of the foraging population of a colony which will work the flowers in question.
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