. Handbook of flower pollination : based upon Hermann MuÌller's work 'The fertilisation of flowers by insects' . Fertilization of plants. RANUNCULACEAE 45 enoughâis thus unfailingly guided, while, at the same time, the length of the cone denies access to shorter-tongued insects. The forwardly directed parts of the same petals prolong the upper part of the hollow cone to the front, and as they expand and turn up anteriorly, they afford a convenient approach to the proboscis of a humble-bee, and also direct it with certainty to the nectar receptacle. These anterior parts of the upper petals sepa
. Handbook of flower pollination : based upon Hermann MuÌller's work 'The fertilisation of flowers by insects' . Fertilization of plants. RANUNCULACEAE 45 enoughâis thus unfailingly guided, while, at the same time, the length of the cone denies access to shorter-tongued insects. The forwardly directed parts of the same petals prolong the upper part of the hollow cone to the front, and as they expand and turn up anteriorly, they afford a convenient approach to the proboscis of a humble-bee, and also direct it with certainty to the nectar receptacle. These anterior parts of the upper petals separate on slight pressure, so that the head of a humble-bee can be entirely thrust between them, thus diminishing the distance to the nectar by 6 to 7 mm. The length of the hollow cone from its entrance to the beginning of the nectar-bearing horns is about 20 mm., and to the ends of the latter 26-28 mm., so that when the head of a humble-bee is thrust into the aperture, its proboscis must be 13-14 mm. long in order to reach the nectar, and 19-22 mm. long to empty the Fig. 16. Delphinium datum, L. (after Herm. Muller). i. Young flower after removal of the petaloid calyx ; front view. 2. The petals in their natural position, seen obliquely from in front and below. 3 Young flower, after removal of the right side of the calyx, seen from the right side. 4. Older flower, after removal of the calyi, front view. 5. Young flower, after removal of the right side of the calyi and corolla, seen from the right side, a a, The two upper petals, which are prolonged backwards into two spurs (a' a") that secrete and contain nectar («), and which in front form an entrance for the humble-bee's proboscis; a' a* bases of the same ; b b, the two lower petals, of which the closely apposed surfaces form the lower boundary of the entrance for the humble-bee's proboscis ; the upper surface of each bears a tuft of yellow hairs to serve as a ^uidc, while between their claws (2.
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