Page:Wayside and Woodland Blossoms.djvu/160

75 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 rostellum and presses it down, touches lightly the viscid feet of the pollen masses (pollinia), and as the pencil is withdrawn both come with it, and stick out from it like a pair of horns.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.