PART III. | THE MECHANISMS OF FLOWERS. 531 
Cryptus (eight specimens belonging to three species) ; (4) Phagedon 
(two); (5) Zryphon (two); (6) Campoplex (one); (7) Microgaster 
rufipes, F. (three). I saw Bombus agrorum, F., licking the honey 
in several flowers without removing the pollinia. 
Sprengel has correctly described how small insects (all of the 
above, except Bombus) regularly alight on the lower end of the 
labellum (p’, 2) and slowly creep upwards licking the honey in the 
groove (v); when they have finished and raise their heads, they 
come in contact without fail with the slightly prominent edge of 
the thin rostellum (7, 1). On the slightest touch, this exudes 
a small white drop of fluid, which reaches the apex of the pollinia 
(po, 1) and hardening instantly, cements them to the object whose 
touch caused the exudation ; and so in every flower which has not 
previously been visited, the insect-visitor receives a new pair of 
pollinia. The insect flies away startled, and soon afterwards alights 
on the labellum of another flower, usually on another plant. The 
rostellum, on first being touched and while it exudes its drop of 
fluid, curves downwards so as partly to protect the stigma (2, 
Fig. 178); but afterwards, while the groove of the labellum is 
secreting a fresh supply of honey, the rostellum gradually rises, 
leaving the way free to the stigma. 
Thus to previous accounts of this flower we may add two 
statements: 1, that when an insect has once attached pollinia 
to its head, it must either acquire a new pair of pollinia or apply 
-some pollen to the stigma in every flower that it visits sub- 
sequently; 2, that not only does cross-fertilisation always occur, 
but that the pollen of one plant is usually carried to a flower 
upon another. 
381. NEOTTIA NIDUS-AVIS, Rich.—The flower resembles that 
of Listera ovata in regard to the function of the rostellum and its 
position in relation to the anther and stigma. It differs, however, 
by concealing its honey from view though leaving it easily 
accessible, by cementing its pollinia to the insect-visitors in a more 
irregular and less effective way, and by being frequently self- 
fertilised owing to the dry pollen falling bit by bit upon the 
stigma. All such insect-visitors as are attracted only by exposed 
honey are absent, and the dull yellow flowers deter all those which 
are only allured by bright colours. 
This tendency to self-fertilisation seems to me to be due athe? 
to the mechanism of the flower being as yet incomplete than to 
scarcity of insect-visits.. I have only once watched this plant at 
MM 2 
