Order VI.—Gynandræ.
By far the greater number of the plants of this order belong to the orchis family (Orchideæ), the second family of the order (Apostasieæ), being a small one and unrepresented in the United States. The orchids are in some respects the most highly specialized of all flowers, and exhibit wonderful variety in the shape and color of the flowers, which are often of extraordinary beauty, and show special contrivances for cross-fertilization that are without parallel among flowering plants.
Fig. 89.—Gynandræ. A, inflorescence of the showy orchis (Orchis spectabilis), × 1 (Orchideæ). B, a single flower, with the upper leaves of the perianth turned back to show the column (x). sp. the spur attached to the lower petal or lip. o, the ovary, × 1. C, the column seen from in front. an. the stamen. gy. the stigmatic surface, × 1. D, the two pollen masses attached to a straw, which was inserted into the flower, by means of the viscid disc (d): i, the masses immediately after their withdrawal; ii, iii, the same a few minutes later, showing the change in position. E, diagram of the flower; the position of the missing stamens indicated by small circles.
The flowers are always more or less bilaterally symmetrical (zygomorphic). The ovary is inferior, and usually twisted so as to turn the flower completely around. There are two sets of perigone leaves, three in each, and these are usually much alike except the lower (through the twisting of the ovary) of the inner set. This petal, known as the “lip” or “labellum,” is usually larger than the others, and different in color, as well as being frequently of peculiar shape. In many of them it is also prolonged backward in a hollow spur (see [Fig. 89], B). In all of the orchids except the lady’s-slippers (Cypripedium) ([Fig. 90], B), only one perfect stamen is developed, and this is united with the three styles to form a special structure known, as the “column” or “gynostemium” ([Fig. 89], B, C). The pollen spores are usually aggregated into two or four waxy masses (“pollinia,” sing. pollinium), which usually can only be removed by the agency of insects upon which all but a very few orchids are absolutely dependent for the pollination of the flowers.
Fig. 90.—Forms of Orchideæ. A, putty-root (Aplectrum), × 1. B, yellow lady’s-slipper (Cypripedium), × ½. C, the column of the same, × 1. an. one of the two perfect stamens. st. sterile, petal-like stamen. gy.. stigma. D, Arethusa, × ½. E, section of the column, × 1: an. stamen. gy. stigma. F, the same, seen from in front. G, Habenaria, × 1. H, Calopogon, × 1. In the last the ovary is not twisted, so that the lip (L) lies on the upper side of the flower.
In the lady-slippers there are two fertile stamens, and a third sterile one has the form of a large triangular shield terminating the column ([Fig. 90], C, st.).