i82 NATIVE BRITISH ORCHIDACE^ 



well as the small keyhole-shaped throat of the flower, showed the influence of 

 0. mascula. Most continental specimens are nearer to O. ?norio. The hybrid is sur- 

 prisingly rare, since the parents grow together so frequently. 



Fertilisation. For detailed account see "Pollination and Fertilisation". 0. mas- 

 cula was the species the study of which enabled Darwin to understand and explain 

 the wonderful mechanism of the flower of Orchis, with all its subtleties of adjustment 

 and accuracy of timing — an achievement all the more remarkable as he had never 

 seen any insects visit the flowers. This was first witnessed by Dr Hermann Miiller 

 on May 6th, 1869, on Stromberg Hill. He saw a humble-bee, apparently Bombus 

 terrestris, alight on the base of a spike of O. mascula, thrust its head into three flowers 

 in succession, and withdraw it in each case with a pair of pollinia attached. It then 

 paused and tried in vain to scrape them off its head. He next saw Bombus hortorum 

 suck three or four flowers of 0. mascula and then go to another spike, on which he 

 found several stigmas pollinated and the anther-cells empty. Within two hours tlitee 

 more visits were observed, two by Bombus lapidarius and one by Psithyrus campestris. 

 These were caught and had a number of pollinia on their heads, some already 

 pointing forwards, in the right position to touch the stigma of the next flower visited, 

 a few still erect. Out of 97 humble-bees caught that day, 32 bore pollinia. It was 

 noticed that when the pollinia had moved downwards, captured bees were sometimes 

 able to tear them off with their mandibles. These occasionally successful efforts 

 explain why pollinia are sometimes found attached to the sepals, petals, etc., by their 

 viscid discs — the bees have succeeded in scraping them off before the cement has 

 had time to set firm. I have on several occasions seen bees succeed in getting rid 

 of pollinia, but only after much effort. Tliis renders untenable the theory of the 

 Italian botanist Delpino that bees visit the flowers of Orchis for the sake of the pollen 

 which they find so conveniently packed for transport ! Quite true, but for transport 

 to another flower, not to the hive or nest. Miiller's observations showed that the 

 three or four seconds spent by a bee on a flower are enough to permit the cement 

 to harden, and to fLx the pollinia firmly to its head, which can easily be confirmed by 

 withdrawing the pollinia from 0. mascula on the point of a pencil. The downward 

 motion is completed in about 40 seconds — very rarely it is accomplished in 25 seconds. 

 A bee spends tluee to four seconds on each flower, and about two in passing from 

 flower to flower. It thus takes about 18 to 22 seconds to visit three or four flowers 

 on a spike, and the bee passes to another plant before the downward motion of the 

 pollinia is effected. There is therefore no danger of a stigma being loaded with pollen 

 from another flower on the same spike, as the pollinia are not in a position to touch 

 the stigma until the downward movement is completed.^ 



The inside of the spur is densely covered with papilla, but quite dry. The outer 



I H. MuUer, Fertilisation of Flowers. 



