2. Dichondreæ. This group is a more primitive form, not twining, and without latex. It has 2 free carpels with basal style (as in Boraginaceæ) and valvate corolla.
3. Cuscuteæ, Dodder Group (Fig. [553]). Parasites, with round, filamentous stems, bearing only scale-like leaves and almost destitute of chlorophyll (they are reddish or yellowish); they are parasitic upon other plants, around which they twine, first with narrow, compact coils from which haustoria (Fig. [553] A) are developed which enter the host-plant, and then with wider coils by which they raise themselves to other portions of their host or try to reach other plants. On germination a very temporary primary root is developed, which bears root-hairs as far as the tip (rootcap is wanting); it only serves as a kind of reservoir for water, and perishes very soon after the seedling has fastened on to a host. The embryo is filamentous and rolled up spirally (Fig. [553] C), and is sometimes destitute of cotyledons. The flowers are crowded into capitulate inflorescences, complicated by accessory shoots (Fig. [553] A); they have S5, P5 (imbricate æstivation), A5 (and beneath the stamens 5 scales on the corolla-tube), G2. Fruit a capsule opening by a lid.—Cuscuta europœa, C. epilinum (Flax-Dodder), C. epithymum (Lesser-Dodder), C. trifolii (Clover-Dodder), etc., are parasitic on different hosts, or parasitic each on its own particular host.
Fig. 553.—Cuscuta trifolii, parasitic on Red Clover. A A portion of the stem with an inflorescence and haustoria (mag.); B seed (nat. size); C seed (mag.); D embryo (nat. size).
840 species; the majority in the Tropics, especially Am. Many are ornamental plants. Officinal: some on account of their purgative properties: the tuberous roots of Ipomæa purga (Jalap, from Mexico) and the dried latex (“Scammony”) of Convolvulus scammonia (from the East). The tuberous roots of Batatas edulis (Trop. S. Am.) are used as a common vegetable (Sweet Potato) in the Tropics.
Family 30. Personatæ.
The type of the flower is: S5, P5, A5 (of which one, or in some cases several, are suppressed), and G2. The flowers are hypogynous, ☿, perfect with gamopetalous corolla, but most frequently irregular (medianly zygomorphic, except Solanaceæ), the corolla being bilabiate (divided into a posterior part of two lobes and an anterior part of three lobes), and the stamens 4, didynamous (the posterior being suppressed). The ovary has 2 loculi (only 1 in Utriculariaceæ, Gesneriaceæ, Orobanche); the placenta in the first-named orders (1–7) is most frequently very thick, and bears a great many ovules (Figs. [554], [555], [557], [562]); the number of ovules in the last orders (8–9) is considerably reduced (Fig. [570]).
Special mention may be made of the apparently 4-merous flower which is found, e.g. in Veronica and Plantago (Figs. [567], [562] C, [570], [571]), and which arises from the typical 5-merous flower by the suppression of the posterior sepal and the posterior stamen, and by the union of the two posterior petals into one.—Terminal flowers very seldom occur on the main axis, and would not harmonise well with the very irregular form of the flower. When they do occur, they are, as a rule, “peloric,” i.e. regular (in Linaria vulgaris two kinds of peloric flowers occur,—one with 5 spurs, and one without spurs). The halves of the anthers are often divided as far as the base, and laterally so widely separated from each other as to assume an almost straight line (Figs. [563], [564]). There is generally a nectary (“disc”) round the base of the ovary, often 5-lobed (or divided into free glands).—A common vegetative characteristic is the absence of stipules.
The 9 orders of the Personatæ are: 1, Solanaceæ; 2, Nolanaceæ; 3, Scrophulariaceæ; 4, Utriculariaceæ; 5, Gesneriaceæ; 6, Bignoniaceæ; 7, Pedaliaceæ; 8, Acanthaceæ; 9, Plantaginaceæ.
