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POPULAR SCIENCE REVIEW. 
forming a body wbicb received from the older botanists the name of the 
“column,” and although, in some cases, these flowers are self-impregnating, 
fertilization is always effected by the escape of the contents of the anther 
cells from the cavities in which they were imbedded, before their contact 
with the stigmatic surface. This, indeed, was understood by Sprengel and 
some other old botanists, but it was reserved for Mr. Darwin to demonstrate 
clearly the process by which the fecundation is performed. The description 
of what takes place in the common orchis ( Orchis mascula ) will serve to 
explain the general nature of these curious phenomena. 
In Orchis mascula , the well-known Purple Orchis of our meadows, the 
stigma is a bilobed viscid surface situated on the front of the pistil ( s , in fig. 1), 
immediately beneath a projecting, pouch-like process ( r ) called the “rostel- 
lum,” above which is the anther ( a ) consisting of two separate cells, each con- 
taining a coherent mass (p) of pollen, or “pollinium.” The pollinia, which, 
when mature, are exposed by a longitudinal slit in the cells containing them, are 
composed of a number of wedge-shaped packets of pollen-grains, united by 
exceedingly elastic, thin threads (see fig. 1, r), which combine towards the 
lower part of each pollinium, to form a straight elastic stalk (c), the “ cau- 
dicle.” The lower extremity of each caudicle is attached to a small disc of 
membrane ( d ) forming part of the superior and posterior covering of the ros- 
tellum. The latter is a nearly spherical projection, which, at an early period of 
its growth, consists of a mass of polygonal cells, which soon become converted 
into two balls of extremely viscid, semi-fluid matter, destitute of all structure, 
lying quite freely within the rostellum, except at the back, where each of 
them adheres to one of the small, membranous discs (e?), already mentioned as 
having the caudicles of the pollinia attached to them on their upper surface. 
These discs are at first continuous with the rest of the membrane enclosing the 
rostellum, but the slightest touch suffices to cause this membrane to split in 
certain definite lines, when, if the membrane of the front of the rostellum is 
pushed down, the two viscid balls which it enclosed are at once exposed. 
This is the mechanism ; its mode of action is as follows : — “ Suppose an 
insect,” says Mr. Darwin, “ to alight on the labellum, which forms a good 
landing place, and to push its head into the chamber at the back of which 
lies the stigma, in order to reach with its proboscis the end of the nectary. 
Owing to the pouch-formed rostellum projecting into the gangway of the 
nectary, it is scarcely possible that any object can be pushed into it without 
the rostellum being touched. The exterior membrane of the rostellum then 
ruptures in the proper lines, and the lip or pouch is easily depressed. When 
this is effected, one or both of the viscid balls will almost infallibly touch 
the intruding body. So viscid are these balls that whatever they touch they 
firmly stick to. Moreover the viscid matter has the peculiar chemical 
quality of setting, hard and dry, in a few minutes’ time.” The same effects 
may be produced by pushing the pointed end of a pencil in the direction of 
the nectary • the viscid balls immediately adhere to it, and as the anther- 
cells are already open in front, the withdrawal of the pencil or of the insect’s 
head, at once removes one or both of the pollinia, which may be pulled out, 
firmly cemented to the object and sticking up from it like horns (fig. 2, a), 
and owing to the position which they occupied in their cells, they diverge a 
little from each other when thus extricated. It is clear that if an insect after 
