OPHRYDEyE—SERAPIADIN^—ACERAS 163 



Fertilisation. The small flowers, the unusually short caudicles, and the two very- 

 shallow depressions in the base of the lip wliich act as nectaries" show that the 

 insects which carry off the pollinia are probably small, but no actual visits seem to 

 have been witnessed or recorded, except as stated below. On a spike of 27 flowers 

 found by me near Gomshall, Surrey, both pollinia had been removed from 1 1 flowers, 

 and one poUinium only from each of four flowers, leaving the second /« sifu in the 

 anther, whilst there was pollen on the stigmas of five flowers. The lower 24 flowers 

 of a long spike found by me near Hyeres, France, had seven flowers with both pollinia 

 removed, three with only one removed, and 14 intact, whilst there was pollen on 

 eight stigmas. This is of special interest as showing that the two pollinia are not 

 attached to one and the same viscid disc, as stated by practically all writers on the 

 subject except Darwin," who recorded that a single pollinium is sometimes removed 

 by insects. On grasping a pollinium with forceps and gently withdrawing it from 

 the anther, the author found, in the case of several flowers thus tested, that it came 

 away with a perfect viscid gland at the foot of the caudicle, quite free from the second 

 pollinium and its viscid disc, wliich remained behind undisturbed. The plant appears 

 to be well visited and fertilised. 



On May 12th, 1928, Colonel G. H. Evans and I watched vases containing cut spikes 

 of Ophrys muscifera on the terrace-wall of the Hotel du Chateau, Challes-les-Eaux, 

 Savoie, France. Amongst them I had placed two or three spikes of A. anthropophora. 

 Ants were running about, and with their usual inquisitiveness, they now and again 

 explored the flowers in the vase. To my astonishment I noticed an ant going down 

 the stalk of Aceras with a pair of pollinia attached very neatly to its head (formica 

 jusca L.). I thought at first this was accidental, but on other days the same thing 

 happened, so it may be concluded that some of the insect-visitors wliich play a part 

 in the pollination of Aceras are certainly ants. Tliis may explain the absence of a spur 

 from tliis plant— the two very shallow depressions in the base of the labellum being 

 admirably adapted for presenting honey to such small creatures as ants. PI. 34, A i. 



They are probably not the only visitors. Hybrids between Aceras and Orchis 

 wiliiaris, simia, purpurea and nndulatifoUa {Italica) are not infrequent, so that the 

 Hymenoptera which visit these latter may also visit Aceras, though of course ants 

 bearing the pollinia of the latter may carry them to the other orchids mentioned. 



The late Mr Burton, of Longner Hall, Salop, told me that while sitting in his 

 glass-house he saw flies {Platychirus ff/anicatus) visiting Aceras, and depositing eggs 

 amongst apliides in the flowers. He watched to see whether they removed pollinia, 

 and in every case found polUnia on their heads. Later he found larvae of Platychirus 

 energetically destroying the apliides. Tliis curious case of the pollination of the 

 flowers of an orcliid through the attraction, not of any product of the plant itself, 



' Darwin, Fert. Orch. ed. 2, p. 26. 



