272 



TAKING UP OF POLLEN BY INSECTS. 



asunder. The first is what occurs in Bartsia al/pina. In the flowers of this plant 

 the entrance is much narrowed, owing to the curving up of the limb of the under- 

 lip, and close behind the entrance are found the anther-valves, which are compara- 

 tively large, and are edged at the top with matted hairs. Before an insect can 

 reach the honey on the floral receptacle it has to force apart the lower edges of 

 these valves, thus letting the pollen fall out upon itself. In the flowers of the 

 Yellow-Rattle and Toothwort {Rhinanthus, Lathrcea), the entrance is still more 

 exactly defined, and the insect cannot deviate a hair's- breadth from it without 

 sustaining injury. The filaments bearing the valves, which in this case are posted 

 in the middle of the entrance, are beset with rigid prickles 

 liable to injure an insect's delicate proboscis, and the only 

 safe path to the receptacle lies between the ciliated anther- 

 valves, which part asunder on being pushed with any 

 moderate force (see figs. 277 *■ ^' ^). In Glandestina, Trixago, 

 and several other Rhinanthacese, the filaments are not fur- 

 nished with prickles, but each anther bears a little down- 

 wardly-directed process which is pushed on one side by an 

 insect entering the flower. The corresponding anthers are 

 parted by the displacement of the processes, and the floury 

 pollen is sprinkled upon the head and back of the intruder. 

 In flowers of the Lousewort genus, — Pedicularis aspleni- 

 folia, P. rostrata, and many species allied to them — the 

 anthers are hidden under the arch of the upper lip, and it 

 is impossible for insects to come into direct contact with 

 them. The path of the insects here lies somewhat deeper 

 between the filaments, which they force apart, causing 

 thereby a corresponding change in the position of all the 

 different parts of the flower. In consequence the anthers 

 also move asunder, and let fall the floury pollen hitherto 

 wedged between them. A somewhat different mechanism is exhibited by several 

 species of the genus Pedicularis, which may be represented by the common 

 alpine Pedicularis recutita (flg. 276). The anthers in the flowers of this plant 

 are borne on elastic filaments, and are regularly squeezed between the lateral 

 walls of the helmet-shaped (galeate) upper lip. No separation of the valves is 

 possible unless the galeate lip expands and becomes laterally inflated. This is 

 brought about in a very curious manner. When a humble-bee alights it seizes 

 the projecting upper lip and bends it down through an angle of about 30°, this 

 action being facilitated by the presence of strong ribs at the base of the helmet on 

 either side of the throat of the corolla which act like levers, and communicate 

 their motion to the entire upper lip. In consequence of the inclination of the 

 upper lip, the sides of the helmet, which up to this time are tightly stretched, 

 bulge out laterally; secondly, the filaments bend in the same sense as the bulging 

 sides of the helmet; and thirdly, the anthers themselves come apart pouring the 



Fig. 276. — Pedicularis recutita. 



1 Entire flower. 2 Longitudinal 

 section of the same. 3 Pol- 

 len falling out in conse- 

 quence of the inclination 

 of the helmet-shaped part 

 of the corolla, x 3. 



