POLLINATION takes place principally by means of insects, but self-pollination occurs in some. The lip serves as a landing-stage for the insect visitors, which, on sucking the honey, cause the adhesive discs, with the pollinia attached to them, to adhere to their bodies (generally to the probosces) and so carry them away to other flowers. In some species parts of the flower are sensitive or irritable, which has some connection with the pollination. Without doubt there are a great many biological differences which are closely connected with the infinite multiplicity of forms; Darwin (1862) has already shown an enormous variety, never even dreamt of before, in the European species. The genus _Catasetum_ has ♂-♀-and ☿-plants with flowers of such different appearances that they have been classed in various genera (_Myanthus_, _Monacanthus_). _Platanthera_ is pollinated by hawk-moths; _Ophrys_, by flies; _Epipactis latifolia_, by wasps; _Orchis_, by bees, especially humble-bees, etc. [Illustration: FIG. 321.--_Chysis bractescens._] The DISTRIBUTION OF SEEDS is effected by the wind, the seeds being so exceedingly small and light. Many species moreover have peculiar, elater-like, fine, hygroscopic hairs in the ovary, which eject the seeds in a manner similar to the elaters of the Liverworts. The USES are few, mostly as ornamental plants in conservatories. The tubers of several _Orchis_-species are OFFICINAL; they contain starch and mucilage and are used us “salep.” The fruits of _Vanilla planifolia_ are used as condiments and differ from other _Orchid_-fruits in being rather fleshy and in dehiscing irregularly; the seeds are very small, shining and black. Class II. =Dicotyledones.= In this class THE EMBRYO has 2 seed-leaves, a rule from which there are few exceptions (_e.g. Ficaria_, _Cyclamen_, _Pinguicula_, certain species of _Corydalis_, with only 1; and a few, mostly parasitic forms, _e.g. Monotropa_, _Orobanche_, _Pyrola_, entirely without cotyledons). On germination the cotyledons nearly always raise themselves above the ground as green, assimilating leaves and are then termed aerial or epigean, in contradistinction to the underground or hypogean which are always buried. The structure of the seed varies (endospermous or exendospermous); the embryo may be straight or curved. In many instances the primary root grows as a vigorous tap-root, with weaker branches arising acropetally (in annuals, biennials, many perennials, especially woody plants); but in a large number of herbaceous perennials, which have rhizomes, the root behaves very much as in the Monocotyledons. The roots generally increase in thickness by means of a cambium.