XI 
THE SPECIAL COLOURS OF PLANTS 
313 
(3) In others there are levers or processes by which the 
anthers are mechanically brought down on to the head or 
back of an insect entering the flower, in such a position as to 
be carried to the stigma of the next flower it visits. This 
may be well seen in many species of Salvia and Erica. 
(4) In some there is a sticky secretion which, getting on 
to the proboscis of an insect, carries away the pollen, and 
applies it to the stigma of another flower. This occurs in our 
common milkwort (Polygala vulgaris). 
(5) In papilionaceous plants there are many complex ad¬ 
justments, such as the squeezing out of pollen from a 
receptacle on to an insect, as in Lotus corniculatus, or the 
sudden springing out and exploding of the anthers so as 
thoroughly to dust the insect, as in Medicago falcata, this 
occurring after the stigma has touched the insect and taken 
off some pollen from the last flower. 
(6) Some flowers or spathes form closed boxes in which 
insects find themselves entrapped, and when they have fertilised 
the flower, the fringe of hairs opens and allows them to escape. 
This occurs in many species of Arum and Aristolochia. 
(7) Still more remarkable are the traps in the flower of 
Asclepias which catch flies, butterflies, and wasps by the legs, 
and the wonderfully complex arrangements of the orchids. 
One of these, our common Orchis pyramidalis, may be briefly 
described to show how varied and beautiful are the arrange¬ 
ments to secure cross-fertilisation. The broad trifid lip of 
the flower offers a support to the moth which is attracted 
by its sweet odour, and two ridges at the base guide the 
proboscis with certainty to the narrow entrance of the 
nectary. When the proboscis has reached the end of the 
spur, its basal portion depresses the little hinged rostellum 
that covers the saddle-shaped sticky glands to which the 
pollen masses (pollinia) are attached. On the proboscis 
being withdrawn, the two pollinia stand erect and parallel, 
firmly attached to the proboscis. In this position, however, 
they would be useless, as they would miss the stigmatic 
surface of the next flow r er visited by the moth. But as 
soon as the proboscis is withdrawn, the two pollen masses 
begin to diverge till they are exactly as far apart as are the 
stigmas of the flower; and then commences a second move- 
