ORDER SILICULOSA. 
167 
CfDited States, and the student can meet with no difficulty in 
procuring them for analysis. 
CLASS XIV. ^TETRADYNAMIA, FOUR STAMENS. 
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 Grucir 
fercB the flowers have four sepals and four petals, each exhibit- 
ing the form of a cross ; hence the term cruciform, from crnx^ a. 
cross. The petals alternate with the sepals ; this alternate po- 
sition is always seen where the number of petals equals the 
number of sepals. The ovary becomes a long jpod^ called a 
silique^ or a short thick one, called silicula : this difference in 
the length of the pods 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 stamens 
arranged in two sets, the 
four at a being longer 
than the two at b ; at 
i are two glands be- 
tween the short sta- 
mens and the ovary : — 
At C is a petal consist- 
ing of a, the border, and 
6, the claw ; at D is the 
pod, which is a silique ; 
a represents the valves ; 
6, the seeds, alternately 
fastened to the edges of 
the partition {dissepi- 
ment), which divides 
this kind of pericarp 
into two cells. The cru- 
ciform plants have dicotyledonous seeds and polypetalous corollas ; the stamens are 
hypogimous. 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 less 
definite than that which marks the orders of the class Didynamia. 
240. The first Order^ Siliculosa^ contains plants which pro- 
duce a short 2indL round pod^ called a silicula i a distinction in 
this order is made between such plants as have pods with a 
239 Class Tetradynamia— Craciform plants— a. Describe Fig. 145.— 240. Order Siliculosa. 
