932. Genus erythronium.—The yellow adder-tongue, or dogtooth violet (Erythronium americanum), shown in [fig. 496], is quite different from any species of trillium. It differs more from any of the species of trillium than they do from each other. The perianth is of six parts, light yellow, often spotted near the base. Stamens are 6. The ovary is obovate, tapering at the base, 3-valved, seeds rather numerous, and the style is elongated. The flower stem, or scape, arises from a scaly bulb deep in the soil, and is sheathed by two elliptical-lanceolate, mottled leaves. The smaller plants have no flower and but one leaf, while the bulb is nearer the surface. Each year new bulbs are formed at the end of runners from a parent bulb. These runners penetrate each year deeper into the soil. The deeper bulbs bear the flower stems.
933. Genus lilium.—While the lily differs from either the trillium or erythronium, yet we recognize a relationship when we compare the perianth of six colored parts, the 6 stamens, and the 3-sided and long 3-loculed ovary.
Fig. 496.
Adder-tongue (erythronium). At left below pistil, and three stamens opposite three parts of the perianth. Bulb at the right.
934. Family Liliaceæ.—The relationship between genera, as between trillium, erythronium, and lilium, brings us to a still higher order of relationship, where the limits are broader than in the genus. Genera which are thus related make up the family. In the case of these genera the family has been named after the lily, and is the lily family, or Liliaceæ.
935. Order, class, group.—In like manner the lily family, the iris family, the amaryllis family, and others which show characters of close relationship are united into an order which has broader limits than the family. This order is the lily order, or order Liliales. The various orders unite to make up the class, and the classes unite to form a group.
936. Variations in usage of the terms class, order, etc.—Thus, according to the system of classification adopted by some, the angiosperms form a group. The group angiosperms is then divided into two classes, the monocotyledones and dicotyledones. (It should be remembered that all systematists do not agree in assigning the same grade and limits to the classes, subclasses, etc. For example, some treat of the angiosperms as a class, and the monocotyledons and dicotyledons as subclasses; while others would divide the monocotyledons and dicotyledons into classes, instead of treating each one as a class or as a subclass. Systematists differ also in usage as to the termination of the ordinal name; for example, some use the word Liliales for Liliifloræ, in writing of the order.)
Fig. 497.