FLY FLOWERS 
the insects when they feel themselves held fast. 
131 
The result is that the pollinia 
fastened to the clips become attached to the visitors, and are thrust into a stigmatic 
cavity by the latter, of course unknowingly and unintentionally. The pollinia stick fast 
to the stigma and remain upon it to effect fertilization 
after the insect has released itself (see Fig. 45). 
Pinch-trap Flowers are not exclusively Fly Flowers, 
though in species of Vincetoxicum, flies of moderate 
size, to the proboscis of which the clips attach them- 
selves, are the agents of pollination. In species of 
Stapelia also, the clips hold on to the proboscis-bristles 
of large carrion-flies, which are attracted by the 
colour of the flowers, and by the well-marked smell 
of decaying flesh. Similarly, in species of Ceropeja 
the pollen is transported by small flies, and here too 
there are little pitfalls in the flower, as in Aristolochia, 
where visitors are retained as prisoners for a time, 
so that these plants form a transition stage between 
Pitfall Flowers and Pinch-trap Flowers. 
In other Pinch-trap Flowers various other insects 
besides flies appear as cross-pollinating agents, On 
the flowers of species of Asclepias, for instance, are 
‘FIG. 45. <Asclepias syriaca, L., 
a Pinch-trap Flower. Flower seen 
from above after removal of sepals 
and petals (x 34):—a, nectar reser- 
voir; 4, conical process of the 
same; ¢c, upper membranous part of 
the stamens; d, outer side of the 
lower part of the stamens enclosing 
the pollinia; ¢, lateral expansion of 
the stamen which with the lateral ex- 
pansion of the neighbouring stamen 
bounds the slit_4 in which the insect's 
foot and later a pollinium is caught. 
to be found, in addition to flies, bees, wasps, fossorial 
wasps, and Lepidoptera, to the claws or limb-bristles of which the clips remain 
hanging (see Fig. 46). In the species of Arauja the clips get attached to the 
proboscis of large bees, while in the species of Stephanotis they are affixed to the 
proboscis of hawk-moths, in which this organ is very long (cf. Delpino—‘Relazione sull’ 
apparecchio della fecondazione nelle Asclepidee,’ Torino, 1865; and‘ Ult.oss.,’ Atti Soc. 
ital. sc. nat., Milano, xi, 1868, 
pp. 224 et seqg.; H. Miller, 
Kosmos, ii, 1877, p. 330). 
The species of Cypripe- 
dium (see Fig. 47) are also 
Pinch-trap Flowers, but here 
the whole insect is seized, 
not merely individual parts of 
the body (proboscis, claws, 
or bristles), as in the flowers 
already mentioned. The visi- ' 
tors may partly be flies, partly the less specialized and less intelligent bees, but in our 
native species—Cypripedium Calceolus—they only consist of the latter. Hermann 
Miiller (Kosmos, ii, 1877, p. 333), however, holds that the purple spots on the upper 
side of the third stamen, which is metamorphosed into a shade for keeping out light, 
are an adaptation originally evolved in relation to flies. 
The labellum, which is deeply excavated like a wooden shoe, bears on its floor 
a coating of juicy hairs, and at the bases of these there are sometimes a few minute 
drops of nectar. Small bees of the genus Andrena try to get into this cavity of the 
K 2 
Fic. 46. Foot of a Lepidopterid with 11 clips (K) and 8 pollinia 
of Asclepias curassavica, 
