THE PRESENTATION OF POLLEN IN CERTAIN ANGIO‐SPERMS AND ITS COLLECTION BY APIS MELLIFERA

Abstract

While investigating the pollen income of a hive of honey bees (Apis mellifera) it was found that some pollen types were collected in abundance, while others were collected rarely or not at all. Moreover, different pollens were collected at different times of the day, and the peak periods in the collection from different species varied strikingly. The first evidence that pollen production and pollen collection were connected was advanced by Synge (I947). The present work is a continuation of the author's previous studies (Percival, I950, I95I). Methods. A small number of plants or, in the case of trees and shrubs, branches was selected. Every flower opening thereon was observed, so that each day a population of flowers in all stages of anthesis was available for examination. The plants were observed throughout the whole, or major part, of their flowering, if this was possible. In some cases the observations were continued in successive seasons. The species usually revealed its rhythm of pollen presentation within a couple of days, but the observations were continued to obtain information on the effect of weather conditions upon it. The unit observed was the 'flower form', whether inflorescence or single flower, but the distinction broke down occasionally, e.g. the inflorescence of Prunus laurocerasus might be taken as the flower form, but observations were also made on the separate flowers. Counts of stamens presenting pollen were taken at hourly intervals if possible. Certain crops (e.g. the Legumes) present their pollen in the bud, so the number of flowers reaching a stage of opening at which the bee could exploit them was noted instead. The opening and closing of the flowers was noted if it occurred within the period of foraging. The data of pollen collection by the bees was taken at the hive or on the crops. All the crops grew near the hives, so any effect of distance on collection could be discounted. Temperature and relative humidity were measured by means of a whirling hygrometer. Periods of sun, rain or overcast were recorded, but air movement was not. Time of presentation of pollen. Most of the species so far studied produce pollen throughout the period 7 a.m.-5 p.m., but the peak period of pollen presentation differs widely (Table i). The longest period of presentation is seen in Helleborus abchasicus, where it is continuous day and night. Aesculus hippocastanum, Pyrus communis, Prunus laurocerasus and