ORDER SILICULOSA. 



167 



United States, and the student can meet with no difficulty in 

 procuring them for analj^sis. 



CLASS XIV. TETKADYNAMIA, FOUR STAIklENS. 



239. We here 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. In the natural order Gruci- 

 ferce the flowers have four sepals and four petals, each exhibit- 

 ing the form of a cross ; hence the term cruciform, from crux^ a 

 cross. The petals alternate with the sepals ; this alternate po- 

 sition is alwaj^s seen where the number of petals equals the 

 number of sepals. The ovary becomes a long pod. called a 

 silique^ or a sJioH thich one, called silicula : this difference in 

 the length of the jpods constitutes the distinction of the two or- 

 ders of the class Tetradynamia, in which they are placed. The 

 cabbage, mustard, radish, and stock-gilly-flower belong to this 

 family. The cruciform tribe is found, on a chemical analysis, to 

 contain some sulphur, and more nitrogen than any other family 

 of plants. 



a. A flower of the 

 cruciform tribe is repre- 

 sented at A, Fig. 145 ; 

 at B are six stameus 

 arranged in two sets, the 

 four at a being longer 

 than the two at b ; at 

 c are two glands be- 

 tween the short sta- 

 mens and tlie ovary : — 

 At C is a petal consist- 

 ing of a, the border, and 

 b, the claw ; at D is the 

 pod, which is a silique ; 

 a represents the valves ; 

 b, the seeds, alternately- 

 fastened to the edges of 

 the partition (dissepi- 

 merit), which divides 

 this kind of pericarp 

 into two cells. The cru- 

 ciform plants have dicotj/ledonous seeds and poh/petalotts corollas ; the stamens are 

 hynogynous. They are herbs, with leaves alternate. The flowers are usually 

 yellow or white, seldom purple. Plants of the class Tetradynamia are never 

 poisonous ; they furnish many important vegetables for the table. The part of the 

 Cauliflower used for food is the deformed or metamorphosed flower-stalks. The 

 distinction in the two orders, depending on the comparative length of pods, is lesa 

 definite than that wliich marks the orders of the class Didynamia. 



240. The first Order ^ Siliculosa^ contains plants which pro- 

 duce a short diYidi round pod^ called a silicula ; a distinction in 

 this order is made between such plants as have pods with a 



Fig. 145, 



239. Clara Tetradynamia— Cruciform plants— ar. Describe Fig. 145.— 240. Order Silicnlosa. 



