Nature may be said to have tried, but not quite fairly, this same experiment; for Orchis pyramidalis, as shown by Mr. Bentham,[1] often produces monstrous flowers without a nectary, or with a short and imperfect one. Sir C. Lyell sent me several spikes from Folkestone with many flowers in this condition: I found six without a vestige of a nectary, and their pollinia had not been removed. In about a dozen other flowers, having either short nectaries, or with the labellum imperfect, with the guiding ridges either absent or developed in excess and rendered foliaceous, the pollinia in one alone had been removed, and the ovarium of another flower was swelling. Yet I found that the saddle-formed discs in the first six and in the dozen other flowers were perfect, and that they readily clasped a needle when inserted in the proper place. Moths had removed the pollinia, and had thoroughly well fertilised the perfect flowers on the same spike; so that they must have neglected the monstrous flowers, or, if visiting them, the derangement in the complex mechanism had hindered the removement of the pollinia, and prevented their fertilisation.
From these several facts I still suspected that nectar must be secreted by our common Orchids, and I determined to examine O. morio rigorously. As soon as many flowers were open, I began to examine them for twenty-three consecutive days: I looked at them after hot sunshine, after rain, and at all hours: I kept the spikes in water, and examined them at midnight, and early the next morning: I irritated the nectaries with a bristle, and exposed them to irritating vapours: I took flowers which had quite lately had their pollinia removed by insects, of which I had independent proof on one occasion by finding within the nectary grains of some foreign pollen; [2] and I took other flowers which from their position on the spike would soon have had their pollinia removed; but the nectary was invariably quite dry.
I still thought that the secretion might perhaps take place at the earliest dawn, as I have found that the secretion of nectar in flowers of other orders ceases and commences in the most rapid manner. Consequently, as O. pyramidalis is visited (as may be seen in the foregoing list) by butterflies and by several day-flying moths (such as Anthrocera and Acontia), I carefully examined its nectary, taking plants from several localities and the most likely flowers, as just explained; but the glittering points within the nectary were absolutely dry. Hence we may safely conclude that the nectaries of the above-named Orchids neither in this country nor in Germany ever contain nectar.
In examining the nectaries of O. morio and maculata, and especially of O. pyramidalis, I was surprised at the degree to which the inner and outer membranes forming the tube or spur were separated from each other,—also at the delicate nature of the inner membrane, which could be most easily penetrated,—and, lastly, at the quantity of fluid contained between these two membranes. So copious is this fluid, that, having at first merely cut off the ends of the nectaries of O. pyramidalis, and gently squeezing them on glass under the microscope, such large drops of fluid exuded from the cut ends that I concluded that the nectaries certainly did contain nectar; but when I carefully made, without any pressure, a slit along the upper surface, and looked into the tube, I found that the inner surface was quite dry.
I then examined the nectaries of Gymnadenia conopsea (a plant ranked by some botanists as a true Orchis) and of Habenaria bifolia, which are always one-third or two-thirds full of nectar: the inner membrane presented the same structure in being covered with papillæ, but there was a plain difference in the inner and outer membranes being closely united, instead of being, as with the above-named species of Orchis, in some degree separated from each other and charged with fluid. Hence I am led to suspect that moths penetrate the lax inner membrane of the nectaries of these Orchids, and suck the copious fluid between the two membranes. I am aware that this is a bold hypothesis; for no case is recorded of nectar being contained between the two membranes of a nectary, [3] or of Lepidoptera penetrating with their delicate probosces even the laxest membrane.
We have seen how numerous and beautifully adapted the contrivances are for the fertilisation of Orchids. We know that it is of the highest importance that the pollinia, when attached to the head or proboscis of an
- ↑ 'Handbook of the British Flora,' 1858, p. 501.
- ↑ I may mention that on soaking and separating the lamime of the proboscis of a moth, which had the pollinia of a Habenaria attached to its head, a surprising number of pollen-grains of some other plant were seen in the water.
- ↑ The nearest approach to this supposed case, yet really distinct, is the secretion of nectar in several monocotyledonous plants (as described by Ad. Brongniart in Bull. Soc. Bot. de France, tom. i. 1854, p. 75) from between the two walls (feuillets) which form the divisions of the ovarium. But the nectar in this case is conducted to the outside by a channel; and the secreting surface is homologically an exterior surface.
