Page:On the Various Contrivances by Which British and Foreign Orchids are Fertilised by Insects, and on the Good Effects of Intercrossing.djvu/90

 species, so that the pollen-masses, when transported by insects from flower to flower, should assume a position fitted to strike the stigmatic surface.

These movements would be quite useless, unless the pollinia first became attached to the insect in a uniform position relatively to the flower, so as to become after the movement of depression invariably directed towards the stigma; and this necessitates that insects should be led to visit all the flowers of the same species in a uniform manner. Hence I must say a few words on the sepals and petals. Their primary function, no doubt, is to protect the organs of fructification in the bud. Even after the flower has fully expanded, the upper sepal and two upper petals often continue the same office. We cannot doubt that this protection is of service, when we see in Stelis the sepals so neatly closing and reprotecting the flower after its expansion; in Masdevallia the sepals soldered together, with two little windows alone left open; and when we see, in the open and exposed flowers of the Bolbophyllum, that the mouth of the stigmatic chamber after a time closes. Analogous facts in Malaxis, Cephalanthera, etc., could be given. But the hood formed by the upper sepal and two upper petals, besides affording protection, evidently forms a guide, compelling insects to visit the flower in front. I do not believe that C. K. Sprengel's view, that the bright and conspicuous colour of the flower serves to attract insects from a distance, is a fanciful notion; though some Orchids have singular inconspicuous and greenish flowers,—perhaps in order to escape some danger. Many of these inconspicuous flowers are, however, strongly scented, which would equally well serve to attract insects.

But the labellum is by far the most important of the external envelopes of the flower. It secretes, and often collects in a receptacle, nectar; or is fleshy, and is furnished with excrescences, which probably are attractive to insects. Unless the flowers were by some means rendered attractive, they would be cursed with perpetual sterility. The labellum always stands in front of the rostellum, and its outer portion often serves, as I have seen, as a landing-place for the necessary visitors: in Epipactis palustris this part is flexible and elastic, and apparently compels insects in retreating to brush against the rostellum: in Cypripedium this end is folded over like the end of a slipper, and compels insects to insert their probosces over and near the anthers. In the older flowers of Spiranthes the labellum moves from the column, and leaves a wider passage for the safe introduction of the pollinia, when attached to the proboscis of a bee. In certain exotic Orchids the labellum suddenly moves and catches insects as if in a box. In Mormodes ignea it is perched on the summit of the column, and here the insects alight and touch the sensitive hinge of the anther. The labellum is often deeply channelled, or has guiding ridges, or is pressed closely against the column, and in a multitude of cases it approaches closely enough to render the flower tubular. By these several means insects are forced to brush against the rostellum. We must not, however, suppose that every detail of structure in the labellum is of use: in some instances, as in Sarcanthus, part of its extraordinary shape seems due to its having been developed in the bud in close apposition to the curiously shaped rostellum.

In Listera ovata the labellum stands far from the column, but its base is narrow, so that insects are led to stand exactly beneath the middle of the rostellum: in other cases, as in Stanhopea, Phalanopsis, etc., the labellum is furnished with upturned lobes, which manifestly act as lateral guides. In some cases, as in Malaxis, the two upper petals are curled backwards so as to be out of the way; in other cases, as in Acropera, Masdevallia, and some Bolbophyllums, these upper petals plainly serve as lateral guides, compelling insects to visit the flower, or to insert their probosces directly in front of the rostellum. In other cases, wings from the margins of the clinandrum, or from the sides of the column, serve as lateral guides both in the withdrawal of the pollinia, and in their subsequent insertion into the stigmatic cavity. So that there can be no doubt that the petals and sepals and rudimentary anthers do good service in several ways, besides in affording protection to the bud.

The final end of the whole flower, with all its parts, is the production of seed; and these are produced by Orchids in vast profusion. Not that this is anything to boast of in the order; for the production of an almost infinite number of eggs, or seeds, is undoubtedly a sign of lowness of organisation. That a plant, not an annual, should escape destruction at some period of its life simply by the production of a vast number of seeds or seedlings, shows a poverty of contrivance, or a want of some fitting protection against some danger. I was curious to estimate the number of seeds produced by Orchids; so I took a ripe capsule of Cephalanthera grandiflora, and arranged the seeds as equably as I could in a narrow hillock, on a long ruled line; and then counted the seeds in a length, accurately measured, of one-tenth of an inch. They were 83 in number, and this would give the whole capsule 6020 seeds; and for the four capsules borne by the plant 24,000 seeds.