. Handbook of flower pollination : based upon Hermann Mu?ller's work 'The fertilisation of flowers by insects' . Fertilization of plants. HYMENOPTERA—BEES i6i The varying length of proboscis is the cause of this difference in habit. B. Gerstackeri ? possesses a proboscis 18-21 mm. in length, with which it can easily suck the nectar from A. Lycoctonum, but the workers, having a proboscis only 11-12 mm. long, are unable to do this. 'There was, therefore, no alternative for the workers but to resort to flowers with less deeply seated nectar, and as A. Napellus corresponds, in regard to nectar, to
. Handbook of flower pollination : based upon Hermann Mu?ller's work 'The fertilisation of flowers by insects' . Fertilization of plants. HYMENOPTERA—BEES i6i The varying length of proboscis is the cause of this difference in habit. B. Gerstackeri ? possesses a proboscis 18-21 mm. in length, with which it can easily suck the nectar from A. Lycoctonum, but the workers, having a proboscis only 11-12 mm. long, are unable to do this. 'There was, therefore, no alternative for the workers but to resort to flowers with less deeply seated nectar, and as A. Napellus corresponds, in regard to nectar, to A. Lycoctonum perhaps more than to any other plant, while at the same time both species are very conspicuous at a distance, and exhibit at the same spot racemes that rival one another in splendour, the division of spoil between queens and workers is not diflScult to explain'.' v. Dalla Torre sees in this ' heterotrophy' an advantage to humble-bees, because it enables the comparatively short lives of these insects to be employed to the best Geographical Distribution Bomhu-j Acunitiim. Fig. 70. Map to iUustraie the distribution of Bontbus and Aconitum (after Kronfeld). With regard to the relation between the distribution of humble-bees and certain flowers that are pollinated by them, Kronfeld (Bot. Jahr., Leipzig, xi, 1890, p. 19), in an interesting paper, points out that the genus Aconitum is dependent upon Bombus. He gives a map showing the areas of distribution of monkshoods and humble-bees, and a glance at this shows that the distributional area of the former is completely included in that of the latter (see Fig. 70). The adaptations of bees to flowers are intimately connected with the length of the proboscis and the other bodily dimensions, for on the former depends, as ' According to Hoffer, the ' heterotrophy' of Bombus Gerstackeri Mor. (in which v. Dalla Torre states that old qneens exclusively visit Aconitum Lycoctonum Z., while males and workers visit A.
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