CLASS TETRADYNAMIA. 



173 



to the four stamens, have a fifth filament, which appears to be the 

 rudiment of another stamen ; sometimes tlie irregular corolla varies 

 into a regular form, with five divisions. Among those which exhib- 

 it the imperfect fifth stamen, are the trumpet-flower, fox-glove, and 

 Penstenion. 



In this order the personate corollas are to be found, or labiate 

 flowers with closed lips. Fig. 137, c, represents a flower of this kind , 

 at d, is the pistil showing the capsule, or that the seeds are aiigio- 

 spermous. It should be oloserved, that in this order some few flowers 

 may be found with bell-form and funnei-form corollas. Plants of 

 this order differ much in their natural characters, from those of the 

 order Gymnospermia. None of them are used in preparations for 

 food, as are the thyme and savory of the first order, but many of 

 them possess powerful medicinal properties, as the fox-glove,* and 

 the cancer-root, (Epiphegns.) They are in general a beautiful col- 

 lection of plants ; few flowers are more splendid than the Gerardia 

 and the trumpet-flower. The Martynia is an exotic of easy cultiva- 

 tion, bearing a fine blossom, while its pericarp furnishes an excel- 

 lent pickle. 



As plants of this class are numerous in every part of the United 

 States, you will have no ditficulty in procuring them for analysis ; 

 they are not usually found in blossom until the middle of summer. 



CLASS XIV. — TETRADYNAMIA. 



In this class we find the cruciform plants, 

 or such as have four petals in the form of a 

 cross; the stamens are six, four of which 

 are longer than the remaining two. The 

 cruciform tribe forms the natural order Cru- 

 cifercn, having flowers with a calyx of four 

 sepals, and a corolla of four petals; each 

 petal is fastened to the receptacle or bottom 

 of the calyx by a narrow part called a claw ; 

 the whole exhibiting the form of a cross ; 

 hence the term cruciform, from crux, a cross. 

 In the centre of the flower is a single pistil, 

 long and cylindrical ; the stigma is oblong 

 and divided into two parts, which are reflex- 

 ed or bent back on each side. Each petal is 

 placed between two leaves of the calyx ; this 

 alternate position is always seen in flowers where the number of 

 petals equals the number of leaves of the calyx. The cruciform 

 flowers have six stamens, two of which standing opposite to each 

 other are shorter than the other four, which always stand in pairs. 

 This inequality in their length determines them to be in the class 

 Tetradynamia. The germ soon becomes a long pod called a silique, 

 or a short thick one, called silicula: this difference in the length of 

 the pods constitutes the distinction of the two orders ot the class in 

 which they are placed. The cabbage, mustard, radish, and stock- 

 gilly-flower belong to this family. They are found, on a chemical 

 analysis, to contain some sulphur. 



Plate vii. Fig. 6. 



Personate flowers — Class Tetradynamia— Describe the cruciform plants. 

 15* 



