260 



BOTANY OF THE LIVING PLANT 



are attractive and conspicuous by their scent, by honey-secretion, 

 and by widely expanded floral envelopes of bright colour. The latter 

 attract the eye, the former the other senses of the animal, and lead 

 him to visit the flower for his own purposes of gathering honey or 

 pollen. Incidentally the floral mechanism is so arranged, in size and 

 form of the parts, that pollen, often of a sticky nature, is deposited on 

 his body as he visits the flower. The flower may be so formed as 

 to lead him, for sake of convenience, to take a definite position : 

 consequently the pollen is deposited on a definite part of his body (Fig. 

 210). The result of repeated visits to a succession of flowers of like 

 construction will then be that, if the stigmas correspond in position 



FIG. 210. 



Pollination of Salvia pratensis. i, Flower visited by Humble Bee, showing the 

 projection of the curved connective from the helmet-shaped upper lip, and the deposit 

 of the pollen on the back of the Bee. 2, Older flower, with connective withdrawn 

 and elongated style. 4, the staminal apparatus at rest, with connective enclosed 

 within the upper lip. 3, the same when disturbed by the entrance of the proboscis 

 of the Bee in the direction of the arrow. /=filament. c=connective. s=the 

 obstructing half of the anther, which produces no pollen. (After Strasburger.) 



to the spots on which he bears the pollen, they may probably receive 

 some part of it. Thus unwittingly he will have been the agent of 

 transfer of the pollen from the pollen-sac to the receptive stigma. 



Such mechanisms have been elaborated in the course of Descent in 

 an infinite variety of detail. This is the biological meaning of the 

 attractive features which flowers have assumed. It may even be seen 

 how certain floral types have been adjusted in relation to the visits 

 of certain animals, and show development parallel with them. A 

 good instance is that of the Aconite and the Humble Bee, to whose 

 visits the Aconite flower offers convenient access. A study of their 

 distribution across Europe and Asia shows that the northern limit of 

 occurrence of the two organisms almost exactly coincides. This 

 suggests the importance of the Humble Bee in the transfer of the 

 pollen of the Aconite, while the food which the flower offers may in 



