541. Its origin. After having imbibed the pollen which the anthers have discharged, the pistil or its ovary continues its growth and enlargement, and is finally matured in the form of the peculiar fruit of the plant. The fruit is, therefore, properly speaking, the ovary brought to perfection.
542. State of the other parts in fruit. The other organs of the flower, having accomplished their work, the fertilization of the ovary, soon wither and fall away. Some of them, however, often persist, to protect or become blended with the ripening fruit. Thus the tube of the superior calyx (§ 446) always blends with the ovary in fruit, as in currant, cucumber, apple, etc. In Composite the persistent limb enlarges into the pappus of the fruit. In buttercups the fruit is beaked with the short, persistent style. In Clematis, Geum, it is caudate (tailed) with the long, growing style. In the Potato tribe, Labiatae, and many others, the inferior calyx continues to vegetate like leaves until the fruit ripens.
543. Consolidated fruit. In some cases the fruit, so-called, consists of the receptacle and ovaries blended, as in blackberry, strawberry. Again, in mulberry, fig, pine-apple, the whole inflorescence is consolidated into the matured fruit.
544. A rule and exception. As a rule, the structure of the fruit agrees essentially with that of the ovary. In many cases, however, the fruit undergoes such changes in the course of its growth from the ovary as to disguise its real structure. An early examination, therefore, is always more reliable in its results than a late one.
545. For example, the oak-acorn is a fruit with but one cell and one seed, although its ovary had three cells and six ovules 1 This singular change is due to the non-development of five of its ovules, while the sixth grew the more rapidly, obliterated the dissepiments by pressing them to the wall, and filled the whole space itself. Similar changes characterize the chestnut, hazelnut, and that whole order. The ovary of the birch is 2-celled, 2-ovuled; but by the suppression of one cell with its ovule, the fruit becomes 1-celled and 1-seeded.
418, Section of the ovary of an acorn, 3-celled, 6-ovuled. 420, Section of ovary of Birch, 2-ce!led, 2-ovuled. 419, Vertical section of the same in fruit. 422. Pericarp of Mignionette open soon after flowering. 421, Naked seed of Taxus Canadensis, surrounded, not covered by the fleshy pericarp.
546. Ox the other hand the cells are sometimes multiplied in the fruit by the formation of false partitions. Thus the pod of thorn-apple (Datura) becomes 4-celled from a 2-celled ovary, and the longer pods of some leguminous plants have cross-partitions formed between the seeds.
Capsule, 427, of Scrophularia, 2-celled; 42S, of Datura Stramonium; 425, of Iris; 426, showing its mode of dehiscence (loculicidal); 424, of Colchicum, 3-celled. 42S, Regma, ripe fruit of Geranium, the carpels (cocci) separating from the axis and bending upwards on the elastic styles.