Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/127

cement is dry the attachment is wonderfully strong. The transparent sides of the rostellum consist of membrane, attached behind to the edges of the boat, and folded over in front, so as to form the anterior face of the rostellum. This folded membrane, therefore, covers, almost like a deck, the cargo of viscid matter within the boat.

Fig. 17.

Spiranthes automnalis, or Ladies'-Tresses.

a.	anther.
p.	pollen-masses.
t.	threads of the pollen-masses.
cl.	margin of clinandrum,
r.	rostellum.
s.	stigma.
n.	nectar receptacle.

A. Side view of flower in its natural position, with the two lower sepals alone removed. The labellum can be recognised by its fringed and reflexed lip.

B. Side view enlarged of a mature flower, with all the sepals and petals removed. The positions of the labellum and of the upper sepal are shown by the dotted lines.

C. Front view of the stigma, and of the rostellum with its embedded, central, boat-formed disc.

D. Front view of the stigma and of the rostellum after the disc has been removed.

E. Disc, removed from the rostellum, greatly enlarged, viewed posteriorly, with the attached elastic threads of the pollen-masses; the pollen-grains have been removed from the threads.

The anterior face of the rostellum is slightly furrowed in a longitudinal line over the middle of the boat, and