i6o NATIVE BRITISH ORCHIDACEyE 



pollinia go through the same downward movement as in Orchis, through an angle 

 of 90°. This movement takes place in about 30 seconds according to Darwin, but 

 I found that in one specimen the pollinia required from li to 2 minutes to complete 

 the movement, which is caused by the sinking down of the front part of the disc 

 till it is separated from the hinder part by an abrupt step.' Darwin was surprised 

 at the degree to which the inner and outer walls of the spur were separated, and at 

 the quantity of fluid contained between them.^ Hildebrand saw this species fertilised 

 by a bee. 



Mr J. Jacob, of Dover, tells me that the man in charge of a colony of Himanto- 

 glossum had continually seen a wasp-like fly {Odynerm parietum) visiting the flowers, 

 but did not notice whether the pollinia were carried ofl^. 



On May 6th, 193 1, not far from Cannes, France, I caught a hive-bee (worker) 

 on H. hircimm bearing seven pollinia, and saw two others come and look at it without 

 alighting. I also saw a smaller bee alight but failed to take liim. 



Genus XIX ACERAS R. Br. 



Column very short, forming a httle chamber, on the roof and walls of wliich is the 

 stigma. Pollinia small, with very short caudicles. Viscid glands two, touching and 

 sometimes coherent, but often separately withdrawn, enclosed in a pouch. Lip 

 without spur. 



Small plants with habit of Orchis. Sepals and petals partly adherent forming a 

 nearly globose helmet. Lip hanging, anthropoid, grooved at base, joined to column 

 by two thick rolls enclosing a shallow cup with two slight depressions. 



AcERAS R. Br. in Ait. Uort. Kew. ed. 2, v, 191 (1815). Ophrys (species) L., Sp. pi. 



p. 948(1753). LoROGLOSSUM(species)Rich.(i8i8). Him antoglossum (species) 



Sprengel (1826). 



Though the genus Aceras owes its name to the absence of a spur, the most important 



character in all previous diagnoses has been the attachment of both pollinia to a single 



viscid disc. Reichenbach f. adopted it as the type of all species with only one viscid 



gland, and transferred to it Anacamptis, Himantoglossum, etc. The two discs lie 



touching each other in the pouch of the rostellum, and sometimes cohere, but are 



frequently removed separately by insects, as I have observed both at home and 



abroad. Darwin pointed this out so long ago as 1862 {Jtert. Orch. p. 26), adding in 



a foot-note: "The separation of this genus is evidently artificial. It is a true Orchis, 



but with a very short nectary". Nevertheless in the most recent works Sclilechter 



and Keller say: " Pollinia ... viscidio rotundato communi affixa",3 and E. G. and 



A. Camus, "retinacles soudes en un seul".* 



I Darwin, Fert. Orch. ed. 2, p. 26. = Ibid. p. 39. 



3 Mon. Orch. Eur. p. 130 (1925). ■> Camus, Icon. p. no (1929). 



