This section is from the book "Wayside And Woodland Blossoms", by Edward Step. Also available from Amazon: Wayside And Woodland Blossoms: A Guide To British Wild-Flowers.
There are nearly forty British species of Orchideae, divided into sixteen genera ; and in the space at our disposal it is impossible to give anything like an adequate account of the group or of the specific characters. An attempt will be made, however, to make the reader acquainted with the general structure by means of three figures. The first of these represents the Marsh Orchis (O. latifolia), a species commonly to be met in wet meadows and marshy places, flowering from May to July. The two tubers are palmate, that is, more or less flattened like a hand, and terminating in finger-like processes. The leaves chiefly spring from the summit of one of these tubers, the lowest acting as sheath for the next, and so on, the tubular flower-stem rising through all the sheaths. The leaves are oblong, and spotted with purple. The inflorescence is a spike, the flowers crowded upon it, but separated by the long three-nerved green bracts. The structure of these flowers will be found to differ widely from all we have considered in these pages. The perianth is placed above the (consequently inferior) ovary, which is twisted. This twist, it will be well to bear in mind, brings the flower "upside down." The three sepals and the three petals are equally coloured, and it is therefore convenient to speak of them as the perianth. There is only one stamen, which is supported by the pistil. Two of the perianth leaves combine to form a hood over the stamen, and a third is greatly larger than the others, divided into three lobes and hanging down like the lip of a labiate flower. This is known as the labellum, and it is continued backwards and downwards as a hollow spur, in which, however, honey is not secreted. At the top of this spur, at the back, is the stigmatic surface, and above it protrudes a fleshy knob, called the rostellum, which supports the anther. This organ consists of two lobes, side by side, which open in front, and reveal in each a mass of pollen grains tied together by elastic threads and attached to a slender foot-stalk with a sticky base. This is a tedious description, though we have made it as brief as possible. The reader shall see the reason for it if he will conduct a little experiment. We may premise that these orchids are fertilized by long-tongued insects, who suck the juice through the tender skin lining the spur.
Now for the experiment. Take a finely-pointed pencil, which we will pretend is the head and tongue of a humble-bee in search of this sweet juice. We push the point gently down the spur, when a part of the pencil touches against the rostel-lum and presses it down, touches lightly the viscid feet of the pollen masses (pollinia), and as the pencil is withdrawn both come with it, and stick out from it like a pair of horns. Be careful to hold the pencil in the exact position it now occupies, and watch. The heavy heads of the pollinia are drooping forward, but after a few minutes they cease to fall lower. Now push the pencil into this other flower. The pollen-masses go directly to the stigma, and some of the pollen is detached. If you are watching where orchids grow it is no uncommon thing to see insects flying around with these pollinia attached to their heads or tongues like a pair of horns.
It will be seen to be impossible for the pollen to fall upon the stigma of the same flower, and from its elastic attachments it is impossible that it should be carried by the wind to another flower, so that insect agency is here an absolute necessity.
Orchis latifolia. - Orchidaceae. -