132 INTRODUCTION 
flower in order to feed on the sap. They use as entry the largest of the three 
passages leading into the cavity which lies in the middle of the gynostemium. 
After having fed well on the juicy hairs, they seek to pass again into the open air, 
but this is not possible by the opening through which they enter, because its edges 
are curved inwards, and are so smooth that the bees always slip down again. The 
two small openings at the back of the flower therefore offer the only chance of 
escape. To these the bee passes, pressing under the stigma and forcing itself into 
Fic. 47. Cypripedium Calceolus, L., a Trap-Flower. (1) Flower seen from above and in front. 
(2) The same in longitudinal section, after removal of the sepals and the two upper petals. (3) Anthers 
and stigma seen from below: a, anthers; a'!, metamorphosed stamen; s, sepal; #, petal; #', specialized 
petal (labellum) ; sé, stigma; ¢, entrance: e2, exit. 
one of the two little exits. In doing so it covers its shoulder with the sticky pollen 
of that anther which forms the inner margin of the exit selected. The bee carries 
the pollen with which it has been thus loaded to the next flower visited, applying it to 
the stigma in the manner described. 
The four or five exotic species of Cypripedium investigated by Delpin (: Ult. oss., 
Atti Soc. ital. sc. nat., Milano, xi, 1868, pp. 175 et seq., xii, 1869, pp. 227 et seq.) are 
Fly-trap Flowers with the same arrangement as Cypripedium Calceolus. According 
to Delpino (op. cit.) Selenipedium is also a Fly-trap Flower of similar construction 
to Cypripedium, ‘ but with this difference, that the two upper of its three floral leaves 
are modified into dependent tails about half a metre long, and these, like other 
similar structures (e.g. in Himantoglossum hircinum), appear to serve as guide-ropes 
to the visiting Diptera.’ (Kosmos, ii, 1877, p. 333-) 
Pinguicula alpina (Fig. 48) possesses a Fly Pinch-trap which is quite different 
from the arrangements of Asclepiads and Cypripedium, and which Hermann Miiller 
describes at length in his ‘Alpenblumen’ (pp. 352-4):— 
