536 
TETRADYNAMIA. 
Class XV. 
Class XV. — TETRADYNAMIA. Stamens 6, of which four are longer than the rest. 
This class consists, with tlie exception of Cleome, entirely of the natural order Cruciferffi, and has lately been 
the subject of the most acute and successful investigation of many botanists of celebrity. Our countryman, 
Mr. Brown, led the way to the improvements which have been made in the genera, in the second edition of the 
Hortus Kewensis, in which, discarding the uncertain and unnatural characters derived from variations in the 
floral envelopes, he took a new course, and by indicating with great precision the curious modifications of the 
seeds and seed-vessels, led the way to an entirely new arrangement of the class. The principles thus developed 
have been adopted by M. Decandolle, whose learned treatise upon Cruciferae is here followed without 
variation. 
The difference between the genera with a long pod {Siliquoscc), and those with a short one (Siliculosce), has 
given rise to two orders in the Linnean system. But these are not only ambiguous, but interfere so much 
with a distribution of the genera according to their natural affinities, that they have been rejected here, and 
the divisions of M. Decandolle, depending upon variation in tlie relative position of the various parts of the 
seed, Iiave been substituted. 
The plants of this class have always been celebrated for their antiscorbutic qualities. These seem to reside 
in an acrid, oily, volatile principle, not yet determined by chemists, and varying in the degree of abundance in 
which it is found in different species. It is particularly abundant in the seeds of mustard and garden rocket, 
in the roots of tlie horse radish, and in the foliage of the Lepidium latifolium, which, administered inwardly, 
act powerfully upon the gastric organs, or, applied externally, inflame the skin and operate nearly as severely 
as blisters. A slighter degree of acrimony is found in the foliage of the scurvy grass, the roots of the garden 
radish, &c. ; and these, therefore, operate more gently, and perhaps more safely, when eaten, scarcely at all 
when applied outwardly. Whatever the degree of acrimony may be in these plants, they all appear, when 
eaten, to produce some specific action upon the digestive organs, and thence upon scorbutic humours ; for 
which reason, the horse radish, water-cress, radishes, and even cabbages are eminently antiscorbutic. They 
are also admitted by physicians as diuretic, sialagogue, and diaphoretic. It is only when the acrid principle is 
diffused over a considerable quantity of fleshy and watery substance, that cruciferous plants become eatable, as 
in the leaves and stems of cabbages and sea-kail, and in the roots of radishes and turnips. Even in these 
plants, the proportion of acrid principle is much diminished by exclusion from light. Plants of this class are 
also remarkable for containing a larger quantity of azote than most vegetables ; for which reason ammonia is 
generally evolved in their fermentation or putrefaction : to which circumstance it is possible that the two 
remarkable phoenomena are to be attributed, viz. ; that cruciferous plants contain a greater portion of nutritive 
matter than most herbaceous plants ; and that they require either a very rich soil manured with animal sub- 
stances, or at least a situation near the habitations of men. Tlie embryos of all these plants are filled with 
oil, and the seeds of Camelina sativa, Brassica campestris, some species of Rocket, &c. are cultivated in many 
parts of Europe for the sake of their expressed oil, which is used either for culinary purposes or for lamps. 
Cruciferous plants are chiefly natives of temperate climates, those which are found within the tropics being 
in all cases mountain plants, and are nearly all cultivable in the open air ; they are mostly found in open 
sandy plains ; some on the tops of the highest mountains at the utmost limits of vegetation. Nine hundred 
species are now described, of which not more than twenty-two are to be found in the works of Hippocrates, 
Theophrastus, Dioscorides, or Pliny. 
A. Cotyledons four, spirally twisted. Petals 4, cruciate. 
1380. Schizopetalon. Petals pinnatifid. 
B. Cotyledons two. Petals 4, cruciate. 
1. Cotyledons flat, accumbenf. Itadicie lateral. Seeds compressed. (0=) Pleurorhize^, Dec. 
* Silique opening ; with a linear dissepiment more or less wide than seeds. Seeds oval, compressed ; 
often tnargined. ' CotyUduns fial, <iccumbefit, parallel with the dissepiment. ArabidejE, Dec. 
1381. i^zihtola. Silique roundish. Stigmas connivent, thickened or cornute at back. Calyx bisaccate at 
liase. . ^ , 
1382. Cheiranthus. Silique round or compressed. Stigmas 2-lobed or capitate. ' Calyx bisaccate at base. 
1383. Nasturtium. Silique roundish, shortened or dec! inate. Stigma nearly 2-lobed. Calvk equal at base, 
spreading. 
1384. Leptocarpeea. Silique roundish, very slender. Stigmas sessile, 2-lobed. Calyx sproadir^g, equal.., 
1385. Notoceras. Silique 4-cornered, 2-edged, the valves elongated at end into a horn or mucro. 
1386. Bar barea. Silique 4-cornered, 2-edged, the valves not elongated at end. Calyx equal at base. 
1387. Braya. Silique oblong, subcylindrical, with flattish valves and a sessile stigma. Seeds few, ovate. 
Calyx equal" at base. 
1388. Parrya. Silique linear with veiny valves. Seeds in two rows, with a loose wrinkled skin. Stigmas 
approximating Filaments not toothed. 
1389. Turritis. Silique linear with flat valves. Seeds in two rows in each cell. 
1390. Arabis. Silique linear with flat valves, 1-nerved in the middle. Seeds in one row in each cell. 
1391. Maa-opodium. Silique pedicellate, linear, with flat valves, 1-nerved in middle. 
1392. Cardamine. Silique linear with flat nerveless valves, often opening with elasticity. Funicles of the 
hilum slender. 
1393. Pteroneuron. Silique lanceolate with flat nerveless valves, often opening with elasticity : placentas 
with winged nerves. Funicles dilated. 
1394. Dentaria. Silique lanceolate with flat nerveless valves, often opening with elasticity : placentas not 
winged. Funicles dilated. 
* * Siiicle opening lengthwise, vSith a broad oval membranous dissepiment, and flat or concave valves. Seeds 
compressed, frequently margined. Cotyledons flat, accumbent, parallel with the dissepiment. Alyssine.e, 
Dec. 
1395. Lunaria. Siiicle pedicellate, elliptical or lanceolate with flat valves. Funicles long, adhering to the 
dissepiment. Calyx somewhat bisaccate. Petals nearly entire. Stamens not toothed. 
Jlicotia. Siiicle sessile, oblong, when ripe losing its dissepiment and becoming 1-celled : valves flat. 
Calyx with two prominences at base. Petals emarginate. Stamens not toothed. 
1397. Farsetia. Siiicle sessile, oval or orbicular, with flat valves. Seeds winged. Calyx bisaccate at base. 
Petals entire. 
1398. Berteroa. Siiicle sessile, elliptical or obovate, with flat or concave valves. Calyx equal at base. Petals 
2-parted. The small stamens toothed. 
1399. Aubrietia. Siiicle oblong with convex valves. Seeds not edged. Calyx bisaccate at base. Petals 
entire. Smaller stamens toothed. 
1100. Vesicaria. Siiicle globose inflated with hemispherical valves. Seeds more than 8. Petals entire. 
