44 NATIVE BRITISH ORCHIDACE^ 



a bait, the lip being really a trap to imprison insect visitors for a time. These cannot 

 escape by the way they came in, owing to the incurled slippery edges of the mouth 

 of the Hp, bees not being able to cling to glass-like surfaces like flies. 



Darwin watched a specimen of Andrena parvula making vain efforts to escape from 

 C. puhescens, but always falling backwards from the polished margins. The only way 

 of escape is by one or other of the two small openings at the base of the lip. To reach 

 these a bee must crawl through the passage roofed by the stigma, which is so low 

 that its back must rub against it. The dry stigma, rough with minute teeth (papillas), 

 acts Hke a rake to scrape off and retain any pollen brought by the bee from some 

 previously visited flower, which in nearly every case is on another plant, as there are 

 rarely two flowers on the same stem. It is therefore an advantage in tliis case to have 

 solitary flowers, as it ensures cross-fertiHsation. 



Miiller considered that the light entering through the above mentioned basal 

 openings guided bees to these exits, and that the staminode screened off the light from 

 the base of the lip, thus making them more visible. The band of hairs on the floor 

 of the hp affords good foothold, and assists bees to crawl up the steep and slippery 

 surface to the only way of escape. Considerable exertion is necessary on the part of 

 the bee to squeeze through the opening. The column being rigid, the stiff but slightly 

 elastic lip has to be forced down a little to make the aperture large enough. Muller's 

 attention was attracted from some distance by the frantic efforts of a small bee 

 {Andrena pratensis) to escape. It tried at least twenty times to get out by the large 

 central opening, but fell back every time. It then went to one of the small apertures, 

 but thought it too narrow. After trying the main entrance and the narrow exits 

 once or twice more, it finally made a determined attempt with great energy at the 

 left-hand small opening, and exerting all its strength at last succeeded in forcing a 

 passage. In doing so its left shoulder was smeared with a good quantity of pollen, 

 for bees cannot avoid rubbing against the convex sticky surface of the anther so 

 cunningly placed in the gangway. 



Muller relates that he visited a colony of about 30 plants of C. calceolm on the 

 Stromberg Hills at 6 a.m. on May 26th, 1868, when the temperature was only 1° C. 

 above freezing-point. In each of three flowers he found a bee in a torpid condition, 

 which had evidently passed the night there. These were so drowsy that when tlorown 

 on their backs they scarcely made an eff"ort to regain their feet. He expresses a doubt 

 as to whether they were stupefied by the scent of the flowers, or merely benumbed 

 by the cold. The latter is the more probable, for, as Darwin pointed out in a letter 

 to Muller, any narcotic eff'ect would cause delay, and render the bees less fit for the 

 transport of pollen, and would thus be a disadvantage to the plant. Muller suggested 

 that the bees possibly used the flowers as a shelter, and in view of the fact that certam 

 species of Serapias in the Mediterranean region appear to be enturely fertihsed by 



