NATURAL GROUPS IN LINNJEAN SYSTEM. 331 



other envelope. We shall hereafter find that the only true 

 naked-seeded plants are the Coniferae or Pine tribe, and its allies, 

 in which the seeds never are enclosed in a seed-vessel. The second 

 Order, Angiospermia, includes those Didynamia which have a 

 distinct seed-capsule, usually two-celled, each cavity containing 

 many seeds. In the next class, TETRADYNAMIA, there are also 

 two orders, distinguished by the form of their pod-like seed- 

 vessel; the first, Siliguosce, having a long-pod; the second, 

 Siliculoscp^ a short one. The Orders of the classes, MONADEL- 

 PHIA, DIADELPHIA, PoLYADELPHiA, depend upon the number of 

 their stamens ; and they have the same names as the first thirteen 

 classes, the number of stamens, however, being never less than 

 five. The subdivision of the class SYNGENESIA (as now under- 

 stood) is rather complex ; and, as it is nearly the same in the 

 Natural System, it will be better explained under the Order 

 Composite. The orders of the classes, GYNANDRIA, MONOECIA, 

 and DICECIA, are distinguished by the number of stamens, and 

 are consequently Monandria^ Pentandria, &c. Those of the class 

 POLYGAMIA are the Moncecia, in which the same plant bears 

 staminiferous, pistilline, and complete flowers ; and the Dicecia, 

 in which these occur on different individuals. 



485. There are many of these orders which form groups truly 

 natural ; that is, which consist of genera having a large number 

 of points of agreement with each other, independently of the 

 characters on which the subdivision is founded. For example, 

 one portion of the class PENTANDRIA, order Digynia, corresponds 

 witli the Natural Order Umbelliferce (including the Parsley, 

 Carrot, Hemlock, Parsnep, &c.) ; the Class TRIANDRIA, order 

 Digynia, very nearly corresponds with the natural group of 

 Grasses, all these having three stamens and two styles, which 

 combination is not found in any other plants. The DIDYNAMIA 

 Gymnospermia, again, are the same with the Natural Order 

 Labiatce, to which belong the various kinds of Mint, Thyme, 

 Dead Nettle, &c. ; and the class TETRADYNAMIA corresponds 

 with the natural Order Cruel/eras, to which belong the Mustard^ 

 Cress, Cabbage, Turnip, Stock, Wall-flower, &c. From the 

 predominance of the number three and its multiples in the parts 



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