After fructification the anthers, stigma, and conducting tissues wither, yet, in many fruits, additions are made to the ovary and its contents by the remains of some of the other parts of the inflorescence. In the apple, which is a simple fruit, the skin of the calyx forms the skin of the apple, and the flesh or edible part is developed out of the ovary and the remainder of the calyx, while the inner layer of the ovary forms the horny cells containing the ripe seeds. In the strawberry, which is a compound fruit, the pulp is the enlarged fleshy receptacle bearing the simple fruit on its surface. In the orange, the membranous partitions of its segments are the linings of the ovary, and the pulp is formed of lax large-celled cellular tissue developed within it.[77] All fruits have the mark of the style; it is very evident in the apple and orange. Simple fruits are formed by a single flower; multiple fruits, like the ananas, or pine-apple, and fir cone, are formed of masses of inflorescence in a state of adhesion. Spiral vessels are frequently found passing from the fleshy part of fruits into the seeds; they are very numerous in the seeds of the Collomia grandiflora and others, coiled up and compressed by the outer skin; but they start to their full length as soon as released. The coats of the seeds of various plants, when seen through a microscope, are beautifully marked. That of the Bignonia is surrounded by a fringe of elongated spiral vessels, the seed of the poppy has a reticulated surface, and many have wings like those of the ash tree, or down like the thistle, that they may be dispersed by the wind. The tendency of roots to strike downwards is so great, that seeds right themselves whichever way they may fall. SECTION XIII. MONOCOTYLEDONOUS, OR ENDOGENOUS PLANTS. THE structure, growth, and reproduction of the flower-bearing vegetation offer objects of the highest interest, though very different from those furnished by the flowerless class. The plants whose seeds have but one lobe form a transition from the lowest to the highest class of vegetables, and include those which furnish the principal articles of food to man and animals. They are all flower-bearing, and consist of numerous families of land and water plants. The most important are the palms, which serve for food in tropical countries, the grasses, which are cosmopolite and social, covering extensive tracts of country with rich verdure, and including the Cerealia, which have been cultivated from such remote antiquity, that the grasses from whence they were derived are unknown. This monocotyledonous class includes, besides the palms and cereals already mentioned, the sugar-cane, the bamboo and other canes, together with reeds, rushes, screw pines, most garden bulbs, the singular and beautiful race of Orchids, and a multitude of other ornamental and useful plants.