THE CLASS MONODELPHIA. 



1C5 



placed at the sides of the others, and the whole are inclosed in a flower, whicn nas 

 invariably four petals, arranged in the form of a Maltese cross, and hence termed 

 Cruciate (Fig. 344). Upon the whole it is a well-defined and arranged class, and 

 may be readily distinguished by the construction of the flower and the pod-like seed 

 vessel which its members possess. It is divided into two orders by somewhat indefinite 

 boundaries viz., Siliculosa, signifying a short pod (Fig. 345) ; and Siliquosa, indicating 

 a long pod (Fig. 346). There are twenty-eight genera and sixty-eight species in the 

 whole class. 



The order Siliculosa is again subdivided into such members as have the pod entire 

 at the top, and others in which the pod is there notched. The former comprehends ten 

 genera, amongst which are the Cochlearia Armoracia or Horse-radish, with other 

 species of tre same genus, Crambe Maritima or Seakale, Cakile or Sea Rocket, and 

 Subularia or Awl-wort ; whilst in the latter there are Thlaspi or Shepherd' s-purse, 

 or Candy-tuft, and Lepidum or Pepper- wort. 



Fig. 344. Tctradynamia. Fig. 345. Siliculosa. Fig. 346. Siliquosa. 



The second order, Siliquosa, contains fourteen genera, and amongst them are plants 

 of greater interest. Thus there is the Brassica (Cabbage, Rape, Turnip, Navew, and 

 Seakale), Sinapis or Mustard, Raphanus or Radish, Nasturtium Oflicinale or Water- 

 cress, Barbarea or Winter Cress, Arabis or Wall and Rock Cress, all of which are 

 useful edible plants ; Cardamine or Ladies' Smock, and other species, Matthiola or 

 Stock, and Cheiranthus or Wall-flower, which are favourite indigenous flowers. 



The class Tetradynamia is therefore ranked amongst the most useful of our vege- 

 table productions, since it supplies much of the green vegetable food used "by man, as 

 well as condiments and aromatic perfumes. The nutritive properties of the Brassica or 

 Cabbage are computed as 1 to 16 of Horse Beans, Lentils, Peas, and Haricots; 1 to 8 

 of Wheat and Oats ; 2 to 1 of Turnips, and of equal proportions to Carrots and old 

 Potatoes ; and is chiefly due to the relative quantities of starch contained within their 

 cells (page 32). 



CLASS XVI. MONODELPHIA. 



This and the succeeding classes are founded upon another feature in connection 



Fig. 348. 

 Monodelphia Polyandria. 



Fig. 347. 

 Monodelphia Pentandria. 



with the stamens viz., the adherence of their filaments, so as to produce one, two, or 



Fig. 349. 

 Monodelphia Deeanclria. 



