POLLINATION 23 



(sap), and suggested that insects visited the flowers for the sake of the pollen, which 

 they find so conveniently packed for transport in pollinia! Anyone, however, who 

 has watched insects with pollinia, will have often seen how hard they try to scrape 

 them off, but rarely with any success, except before the viscid matter has had time 

 to set hard. Whether the fluid secreted be, as Delpino suggested, merely acqua di 

 traspira^ione or sap, it is certain that bees of various kinds are attracted. One often 

 comes across a tiny trickle of water on sandy ground, with numbers of bees eagerly 

 quenching their tliirst. In most places such trickles are rare, and the hquid contained 

 in the spur of Orchis is probably sought to satisfy thirst. Darwin mentions 10-16 

 poUinia found on hive-bees visiting 0. morio. I have watched humble-bees searching 

 out msignificant little plants of Pediadaris palmtris evidently for honey, but entirely 

 ignoring the more abundant and much more conspicuous flowers of O. mrio. Never- 

 theless I saw some visiting 0. morio, and the number of fertilised ovaries showed 

 that visits must have been much more frequent on other days. Honey-collecting must 

 be thirsty work on a hot day, and Orchis flowers very convenient drinking fountains 

 A few species— relatively very few— are self-fertilised. In almost every case the 

 faculty of self-pollination appears to have been subsequently added to a flower already 

 orgamsed for cross-poUination by means of a rosteUum, and the two processes exist 

 concurrently. Thus in Cephalanthera grandiflora if the poUinia are not removed by 

 insects, they crumble and fall on the stigma. This occurs so often that the species is 

 commonly regarded as always self-fertilising. As will be seen later it is visited by at 

 least two species of Hymenoptera. In Epipactis kptochila Godf. and E. dmmisis Godf 

 there is a rosteUum when the flower first opens, but it disappears by the time the next 

 flower unfolds, and often fafls to develop at aU. A good deal of pollen, however 

 shdes over the slopmg upper edges of the stigma on to its eff-ective surface. In the 

 contmental E. Muelleri Godf. the anther base projects well over the base of the stigma 

 which IS there horizontal, and deposits the poUinia directly on its sticky surface. There 

 IS no rosteUum, but in bud there is a rounded protuberance in the middle of the upper 

 edge of the stigma which looks like a rudimentary rosteUum, and a few drops of 

 nectar are secreted in the basal cup of the Up. In Neottia nidus-avis, if the poUinia are 

 not removed, some of the poUen finds its way over the rosteUum to the stigma 

 Ophrjs apifera habitually pollinates itself {q.v.), but the machinery for the removal of 

 the poUima is stUl m perfect working order, and hybrids arise between it and other 

 species. Mr C. S. Garnett, F.L.S., of Derby, saw several bees visiting the flowers 

 in 1930. Neotima tntacta is also self-poUinating, but the poUinia are attached to viscid 

 discs kept moist m the pouch of the rosteUum, and can be withdrawn on a bristle— 

 with difficulty, it is true, as they are so minute. There is free honey in the spur but 

 so far there is no record of insects having been seen visiting the flowers. Five 

 British species are partly self-fertUising, most of them mainly so. 



