Sepals 4, deciduous, cruciate, the lateral ones gibbous, or spurred at the base. Corolla hypogynous, cruciform, petals 4, alternate with the sepals, deciduous, stamens 6, the two, opposite the lateral sepals, shorter, and occasionally toothed, 4, in pairs, opposite the anterior and posterior sepals, longer : anthers bilocular, introrse. Torus with several glands between the petals and the stamens, and the ovarium. Ovary usually bilocular with parietal placentas, generally, meeting in the middle, and forming a spurious partition, stigmas two opposite the placentas. Fruit a siliqua orsilicule, rarely one-celled and indehiscent, usually opening by two valves separating from the placentae. Seeds attached in a single row, by a funiculus, to each side of the placentas, generally pendulous. Albumen none, embryo with the radical folded up on the cotyledons : if on the edge they are said to be accumbent, if on the back incumbent, sometimes the cotyledons are folded, they are then said to be conduplicate incumbent, &c. (In Nasturtium they are accumbent, in Lepidium incumbent, the cotyledons in the latter 3-lobed.)
Affinities. The nearest affinities of this order are with Capparidere, agreeing in the quaternary number of the divisions of the flower : in the fruit having two placentae, and a similar mode of dehiscence ; and in the stamens of some species of the Capparidece, agreeing in number. They have also some affinities with Fumariacece as already shewn under that order, but are kept distinct by the different structure of the seed.
Essential Character. Flowers polypetalous, stamens tetradynamous. Ovary wholly superior, the carpels combined into a solitary pistillum : seeds without albumen. Leaves alternate, destitute of stipules.
Geographical Distribution. I have remarked above that the species of this order are very rare within the tropics. Europe indeed maybe esteemed the head quarters of Cruciferce $ but they are abundant all over the temperate zone of the northern hemisphere, and comparatively rare in the southern : upwards of 600 appertaining to the one, and scarcely 100 to the other. But to enter into minute details of the geographical distribution of an almost extra Indian order in a work on Indian Botany, can be of but little avail ; I may however observe, that many are cultivated both for use and ornament in this country, and it seems not improbable, that the number might be increased, at least during the cool season, owing to most of them being annual, and requiring in this country but a few months to attain maturity. Whether attemps for their naturalization will ever so far succeed on the plains as to render us independent of more temperate climates for our supplies of seed, is a question still to be solved, but one, the solution which, when we consider their value to mankind, ought not to be readily relinquished, even though the chances against success, appear to preponderate. If this desirable object is ever to be accomplished, it must undoubtedly be through gradual extension from the more elevated and cooler regions, to the lower and warmer ones. One source of disappointment, viz. the oily nature of their seed, is not easily guarded against, as oily seeds generally soon deteriorate, and I presume more rapidly in a warm climate : while, owing to the long interval that intervenes between their arrival at maturity, and the period for sowing, they are exposed so much the more to this source of deterioration.
Properties and Uses. Acrimony, more or less combined with bitterness, forms the predominant quality of the Cruciferce, in proof of which it is only necessary to mention, Horse-radish, Mustard, Cress, the common Radish, and Water-cress, all of which possess this property in an eminent degree, and even the cabbage, now so much used when ameliorated by cultivation, as aliment, possesses in its wild state much of the acrid properties inherent in the family. The principle on which their acrimony depends is of a volatile nature, and is greally diminished by drying. Formerly it was attributed to the presence of volatile alkali, but careful chemical analysis proved the erroneousness of this opinion, by showing the total absence of ammonia, in the recent state of these plants, or in, their expressed juices, though, during the process of putrefaction, it is exhaled in considerable quantity : hence it must be generated during decomposition, and is attributable to nitrogen, which enters largely into their composition. The more prevalent opinion now is, that their acrimony owes its existence to the presence of volatile oil, an opinion resting on a better foundation, though reasoning from analogy,
