RANUNCULACEAE 



45 



enough — is 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 receptacle. 



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 nectar .i^uidc, while between their claws (2. b' b") is an mterval {2. b') m which the anthers 

 and stigmas successively appear (in the two stages of flowering), and which is in the path of the insect's 

 proboscis ■ c dehisced anthers placed behind the entrance to the spur m the path of the insect's proboscis ; 

 d anthers' which have not yet dehisced, and are bent downwards over the lemale organs ; e, surface of 

 attachment of the stamens and carpels (which have been removed) ; /, withered stamens bent downwards ; 

 fr ovaries ■ A stigmas, which have placed themselves in the same spot that the ripe anthers occupied 

 iti the first stkge ; /, left half of the upper sepal, prolonged backwards into a corrugated sheath (i') 

 for the spur ; A, left lateral sepal ; /, left lower sepal. (3 and 5 natural size ; i, 2, and 4 enlarged.) 



There are bundles of erect yellow hairs upon the front surfaces of the two lower 



petals serving as nectar-guides— which are here closely apposed, thus bounding below 



the way of entry to the nectar, and obliging humble-bees to probe in the only right 

 place. The claws of these petals, on the other hand, are sufBcienlly far apart to 

 enable the stamens and — after they have withered and bent back— the carpels to 



