THOMAS THE YELLOW LADY'S SLIPPER 265 



tion is accomplished. The basal part of the labellum is folded 

 round the short column so that its edges nearly meet along the 

 dorsal surface, and the broad extremity is folded over in a pe- 

 culiar manner, the overarching edges being inflected or sometimes 

 only smooth and polished internally. This is of much impor- 

 tance, as it prevents insects which have once entered the labellum 

 from escaping thru the great opening in the upper surface. There 

 is but one means of escape, namely, by way of one of the two orifices 

 in the labellum close to the column. Let us follow the path of a 

 small bee: — Finding it impossible to escape by the large opening, 

 she crawls up into the narrow passage towards the smaller port- 

 holes admitting daylight into her prison. Here she must creep 

 under the stigma w^hich protrudes its convex surface as a low 

 ceiling to this cell which is only large enough to admiit her body. 

 The surface of the stigma is beset with minute, rigid, sharp- 

 pointed papillae, directed forward, which are excellently adapted 

 to brush' off any pollen which may have adhered to the insect's 

 head or back while visiting another flower. Her way is now clear 

 to freedom, but just before emerging she must pass by the anther 

 which stands behind and above the lower surface of the stigma. 

 The grains of pollen are coated by and immersed in a viscid 

 fluid, which is so glutinous that it can be drawn out into short 

 threads. This pollen has but to be touched to adhere to the 

 bee's head or back, so that tho it can be carried quite readily to 

 another flower, there is no way in which it could be brought in 

 contact with the stigmatic surface of the same flower. 



Darwin tells most interestingly of his experiments in the fer- 

 tilization of C. pubescens. He says, 'T first introduced some 

 flies into the labellum thru the large upper opening, but they 

 were either too large or too stupid, and did not crawl out properly. 

 I then caught and placed , within the labellum a very small bee 

 which seemed of about the right size, namely, Andrena parvula, 

 and this by a strange chance, proved to belong to the genus on 

 which in a state of nature the fertilization of C. calceolus depends. 

 The bee vainly endeavored to crawl out again the same way by 

 which it had entered, but always fell backwards, owing to the 

 margins being inflected. The labellimi thus acts like one of those 

 conical traps with edges turned inwards, which are sold to catch 

 beetles and cockroaches in London kitchens. It could not creep 

 out thru the slit between the folded edges of the basal part of the 



