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CLASS 15. TETRADYNAMIA. 



(Containing Plants ivith four long and two short Stamens.) 

 Flowers of four Petals, opposite each other. 



This class is the same as the natural order Cruciferse or 

 the Cruciform plants, so called because all belonging to it 

 have their four petals arranged in a cross : they also bear 

 their seeds in a short or long pod-shaped seed-vessel. The 

 properties of the whole are very similar, they assist digestion 

 greatly, and purify the blood. There have been discovered 

 about nine hundred different species belonging to the Cruci- 

 form tribe, which for the most part grow in the temperate re- 

 gions of the earth. England produces about seventy of these 

 species, some of which are well known, either as eatable vege- 

 tables or as garden flowers ; among them are the Sea Kale, the 

 Mustard and the Cress, the Cabbage, the Turnip, the Radish, 

 the Horse-Radish, the Woad, (which was the plant used by 

 the Ancient Britons in dyeing their skins blue,) the Water- 

 Cress, the Candy-tuft, the Wallflower, the Stock, the Gold 

 of Pleasure, and the Rocket, or Dame's-violet, which is 

 scentless all day, but fragrant in the evening. 



Order 1. SILICULOSA. 



Seed-vessel a short pod or pouch. 



WART-CRESS, (Coronopus.) Pouch two-lobed, seeds two. 



SHEPHERD'S PURSE, (Capsella.) Pouch heart-shaped, seeds 

 many. 



SCURVY- GRASS, (Cochlearia.) Pouch round, swelled, many- 

 seeded* 



WHITLOW-GRASS, (Draba.) Pouch oval, flat, many-seeded. 



