from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A small beaklike part, such as a projection on the stigma of an orchid, a tubular mouthpart on some insects, or the hooked projection on the head of a tapeworm.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A small beak-like process or extension; a small rostrum.
from the GNU version of the Collaborative International Dictionary of English
- n. A small beaklike process or extension of some part; a small rostrum
from The Century Dictionary and Cyclopedia
- n. In botany: Any small beak-shaped process, as in the stigma of many violets; specifically, a modification of the stigma in many orchids, which bears the glands to which the pollen-masses are attached.
- n. A Linnean term for the caulicle or radicle.
- n. In zoology, the fore part of the head of tapeworms or other cestoids, bearing spines or hooklets which are said to be rostellar. See cut under Cestoidea.
- n. [capitalized] [NL.] In conchology, same as Rostellaria.
- n. The combined mouth-parts of the true lice, of the family Pediculidæ.
The scolex of the organism is globular in shape and features a prominent projection known as a rostellum that is lined with a double row of hooks.
The splitting of the rostellum, curiously enough, never happens without insect aid; but if a bristle or needle be passed over it ever so lightly, a stream of sticky, milky fluid exudes, hardens, and the boat-shaped disk, with pollen masses attached, may be withdrawn on the bristle just as the bee removes them with her tongue.
As nectar is already secreted for her in its receptacle, she thrusts her tongue through the channel provided to guide it aright, and by the slight contact with the furrowed rostellum, it splits, and releases a boat-shaped disk standing vertically on its stern in the passage.
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.
If you could prove what I only conjectured (from state of utriculi in rostellum and in stigma of Catasetum and Acropera) that the utriculi somehow induce, or are correlated with, penetration of pollen-tubes you will make an important physiological discovery.
So in other cases, but I have not completely traced (only seen) that going to the rostellum.
By the way, Cephalanthera has single pollen-grains, but this seems to be a case of degradation, for the rostellum is utterly aborted.
Read Asa Gray in 2nd Review of my Orchis book on pollen of Gymnadenia penetrating rostellum.
I want to know whether anything beats in modification the rostellum of Catasetum.
I will say nothing about the rostellum, stigmatic utriculi, fertility of Acropera and Catasetum, for I am completely bewildered: it will rest with you to settle these points by your excellent observations and experiments.