ii6 Flowers and their Unbidden Guests. 



flower to flower, to promote intercrossing. Should 

 it, however, not pass in by the mid-lohe, but make 

 its approach from the side, it will be under the 

 necessity of crossing over one of the two hollow peg- 

 shaped projections which are developed on the lower 

 lip ; or possibly as these hollow projections — which 

 have given the plant in Germany the name of Hohl- 

 zahn — form fair landing-places, the insect may alight 

 directly upon one of them, and then pass down by 

 its hinder slope into the recesses of the flower. But 

 as the apex of each of these projections is not more 

 than 2'5 mm. distant from the anthers and the stigma, 

 insects of this thickness, in cHmbing over them, will 

 rub against the stigma and the pollen. Suppose, how- 

 ever, that there were no hollow projections; suppose 

 that in place of them there were actual furrows, as there 

 are in the same position in so many other Labiatse. 

 The distance between the anthers and the spot where 

 the projections stood would now be not merely 2'5 

 mm. but 4 mm. or more. Small insects, therefore, with 

 a body not more than 2 '5 mm. in thickness could reach 

 the tube and carry off the nectar, without ever touching 

 the pollen, without therefore conducing to allogamy, or 

 repaying to the plant the price of its honey. 



Another very striking instance of a corolla contracted 

 by tubercles is furnished by the flowers of Scutellaria. 

 In Bcuitdlarwb albida L. (Plate II. fig. 58, longitudinal 

 section of corolla; fig. 59, central view, lower lip re- 



