444 SYSTEMATIC BOTANY. 



the seed, in the fonns of Myronic acid and Myrosyne. These substances, 

 when mixed through the medium of water, foim the volatile oil of black 

 mustard. The active properties of white mustard-seeds are not due to the 

 presence of a volatile oil, as no such oil can be obtained from them by distil- 

 lation with water, or otherwise ; but they are owing to a fixed pungent and 

 acrid principle, which does not pre-exist in the seeds, but only its elements 

 in the form of Sinapiu or Sinapisin, and a substance resembling vegetable 

 albumen or emulsin. These, when brought together under the influence of 

 water, produce the fixed acrid principle of white mustard seeds. Internally, 

 flour of muE-tard is used as a stimulant, diuretic, and emetic ; and externally 

 applied, it is irritant, rubefacient, &c. The volatile oil is a powerful 

 vesicant. White mustard seeds are also taken in an entire state as stimu- 

 lants in dyspepsia. The seeds of Sinapis juncea, a native of India, possess 

 similar properties to those of Black and White Mustard seed. 



Many plants of the order are favourite objects of culture in our gardens, 

 such as the Stock (Matthiola), Wallflower (Cheiranthus Cheiri), Candy Tuft 

 {Ibeiis umbellata), Honesty {Lunaria biennis), &c. 



Natural Order 16. Cappaeidace^. — The Caper Order. — 

 Character. — Herbs, shrubs, or rarely trees. Leaves alternate, 

 exstipulate, or rarely with spiny stipulate appendages. Sepals 

 4 (fgr. 642, cal), sometimes cohering more or less ; (estivation 

 imbricate or valvate, equal or unequal. Petals usually 4 (fig. 

 642, cor), cruciate, imbricate, generally unequal and unguiculate. 

 rarely 8, or sometimes none. Stamens numerous, or definite, 

 (if 6, very rarely tetradynamous), placed usually upon a prolonged 

 thalamus or stalk by which they are raised above the corolla {fig. 

 642, st). Ovary placed on a gynophore {fig. 642, ov), or sessile, 

 1 -celled ; 'placentas 2 or more, parietal ; style filiform or wanting ; 

 ovules amphitropal or campylotropal. Fruit 1 -celled, usually 

 many-seeded, very rarely 1 -seeded, either pod-shaped and dehis- 

 cent, or baccate and indehiscent. Seeds generally reniform, with- 

 out albumen ; embryo curved ; cotyledons leafy. 



Diagnosis. — Herbs, shrubs, or trees, with alternate leaves. 

 Sepals and petals 4 each, the latter cruciate, and generally 

 imequal. Stamens usually numerous, very rarely tetradynamous, 

 usually inserted on a stalk, which raises them above the corolla. 

 Ovary 1 -celled, placentas parietal. Fruit dehiscent or indehis- 

 cent, 1 -celled. Seeds generally reniform; embryo curved; no 

 albumen. 



Division of the Order, and Examples of the Genera. — The order 

 is divided into two sub-orders, according to the nature of the 

 fruit, as follows : — 



Sub-order 1. Cleomea. — Fruit capsular and dehiscent. Ex- 

 amples : — Grynandropsis, Cleome. 



Sub-order 2. CapparecB. — Fruit baccate and indehiscent. Ex- 

 amples: — Cadaba, Capparis. 



Distribution and Numbers. — The plants of the order are chiefly 

 found in tropical and sub-tropical regions of the globe. In 

 Africa they are especially abundant. The common Caper {Cap- 



