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Siliquosæ and Siliculosæ
In the seed, the radicle and cotyledons are applied to each other in different ways, from which the suborders of M. Decandolle derive their characters. When the edge of the cotyledons is pressed close to the radicula, so that a cross section would be thus, the cotyledons are said to be accumbent, as in all Pleurorhizeæ; when the side of the cotyledons is pressed to the radicula thus ○ 11, the former are called incumbent, as in Notorhizeæ. If the cotyledons are incumbent, and at the same time half folded together or conduplicate, thus O>>, the suborder Orthoploceæ is formed; when the cotyledons are incumbent and spirally twisted, so that a section would resemble this O 11 11, they constitute the suborder Spirolobeæ; and finally, when the cotyledons are incumbent, and doubled twice in their length, thus O || || 11, we have Diplecolobeæ.
The whole order is preeminently European; 166 species are found in the north and middle of Europe, and 178 on the sea-shores of the Mediterranean; 45 are found between Mogadore and Alexandria; 184 in the countries of the East, that is to say, Syria, Asia Minor, Tauria, and Persia; 99 in Siberia; 35 in China, Japan, and India; 16 in New Holland and the South Sea islands; 6 in the Mauritius and adjacent countries; 70 at the Cape; 9 in the Canaries; 2 in Saint Helena; 2 in the West Indies; 41 in South America; 48 in North America; 5 in Kamtchatka and the bordering islands; and finally, 35 are common to several parts of the globe. From this it appears that there are about 100 species in the southern hemisphere, and about 800 in the northern: or, if they are considered with reference to the zones of temperature, 205 are natives of the frigid zone of the northern hemisphere; 30 of the whole of the tropics; 548 of the temperate zone of the northern hemisphere; and 86 of the southern. The forty-first degree of north latitude may be considered the equa- NATURAL ARRANGEMENT. torial line of Cruciferæ, about half being found on one side of it, and half on the other. Their station is very variable; many inhabit open sandy places, some form the vegetation about the limits of the perpetual snows of lofty mountains, and many follow the footsteps of man through all parts of the world. The useful qualities of the turnip, the radish, the rape, and the cabbage, and its multiform varieties, are all well known. The greater part of the order consists of plants possessing high antiscorbutic powers. These appear to depend upon a certain acrid volatile oily principle, the chemical nature of which is imperfectly known. It is particularly abundant in the seeds of mustard and the roots of horseradish, and the leaves of Lepídium latifólium, which latter exercise a violent influence upon the organs of digestion. The same sort of acrimony, but in less degree, is found in the herbage of the scurvy-grass and the roots of the radish, which act much more mildly when taken inwardly; thus, when any cruciferous plants are found to be eatable, either from culture or other circumstances, it is to be understood to depend upon a reduction of this acrid principle. The exciting powers of this last, are what render the horse-radish, the scurvy grass, and others, so remarkably useful as antiscorbutics; they are also believed to possess diuretic and diaphoretic properties. It is to be remarked, that Cruciferæ are always eatable when their texture is succulent and watery, as in the roots of the radish and the turnip, and the leaves of the cabbage tribe. A further diminution of the acrid principle is produced by blanching. Cruciferæ are said to possess a greater share of azote than any other tribe of plants; as is apparent in their fetid smell when fermented. The embryo of all the order abounds in oil, whence many species are employed with much advantage for expressing, either for eating or for feeding lamps. Some of the species are extremely beautiful and fragrant, as the Stocks, the Gillyflowers, the Hesperides, the Candytufts, and many others. The Hutchinsias, Drabas, Cardamines, &c. are among the most interesting of alpine plants 1381 Mathiola R. Br. 1382 Cheiránthus L. 1383 Nastúrtium R. Br. 1384 Leptocarpæ'a Dec. 1395 Lunária L. 1396 Ricótia L. 1397 Farsétia Turr. 1398 Berteróa Dec. 1408 Thláspi L.