1 70 TETRAD Y N AM IA. 



CLASS XV. TETR ADYNAMIA. Stamens 6. 4 long, 

 short. Orders 2. 



The name of this class comes from tetra, 

 four, dys, two, and nema, a filament, and in 

 its present application means, that the flowers 

 which belong here must have six stamens, 

 two of which are shorter than the others. 

 This is considered among the most natural of 

 all the Linnaean classes. It is, indeed, with 

 the exception of a single genus, (Cleome,) an 

 entirely natural tribe, consisting wholly of 

 cruciform flowers, as Cabbage, Mustard, &c. This class 

 has usually been divided into two orders, founded on the 

 length of the pod which the genera presented. The order 

 Siliquosa, including such fruit as consisted of a long pod, and 

 Siliculosa, such as presented a short one. Now these distinc- 

 tions are not only ambiguous, and often very perplexing, (for 

 we cannot distinguish by the flower, as is usual, where a 

 specimen belongs, but must wait for the fruit,) but they also 

 prevent the distribution of the genera according to the natural 

 affinities. These orders are therefore rejected by M. Decan- 

 dolle, and other botanists, and other divisions substituted, 

 depending upon variations in the relative position of the vari- 

 ous parts of the seed, and seed vessels. 



Our present purpose will be answered by omitting to ar- 

 range the genera with reference to the above named orders. 

 And by omitting the distinctions of M. Decandolle, also, we 

 shall lessen the perplexity, and add to the comfort of our stu- 

 dents. We should, however, recommend to them a more 

 intimate knowledge of this class than can here be obtained. 

 Among the most common plants of this class, are Lunaria, 

 (Satin flower,) Raphanus, (Radish,) Brassica, (Turnip and 

 Cabbage,) Sinapis, (Mustard,) Lepidium, (Peppergrass,) 

 Thlaspi, (Shepherd's Purse,) Sisymbrium, (Hedge Mustard,) 

 Cheiranthus, (Wall Flower,) and Nasturtium, Water Cress. 

 GENUS Nasturtium. The name, according to Pliny, 

 comes from nasus torsus, convulsed nose, in allusion to the 

 effect it produces on the nose when eaten. In England tho 



How may a plant of the class Tetradynamia be known by its stamens ? 

 What is said of the former divisions of this class? What are the names 

 of some of the plants belonging to this class ? 



