178 
CLASS DIADELPHIA. 
i 
LECTURE XXXIII. 
CLASS XVI. — DIADELPHIA. 
This is the class of two brotherhoods, the 
stamens being united by their filaments into 
two sets. The flowers of this class are Papi- 
lionaceous^ or butterfly-shaped ; this peculiar 
form of their corollas is an important mark of 
distinction. 
Two circumstances should be noted here, 
in order to prevent you from falhng into error 
with respect to this class. 
1st. There are some plants with filaments 
united in one set, but with flowers papiliona- 
ceous ; these are retained in Diadelphia, though 
there be no apparent division in the brother- 
hood or set. 
2d. Though the flower be papilionaceous^ if it have ten separate 
stamens, it is placed in the 10th class ; this is the case with the cas- 
sia and wild indigo. 
Linnaeus, in reference to the form of the flowers, arranged this 
tribe under a natural order Papilionacece j — Jussieu, regarding the 
fruitj called the same LeguminoscE. 
Papilionaceous Flowers. 
Fig. 142 repre- 
sents the sweet pea 
{Lathy rus odor a- 
ius ;) at a, is the 
five-toothed calyx ; 
at 6, is the upper 
petal, called the 
banner ; at c, are 
the wings, or two 
side petals ; at d, is 
the keel, formed of 
two petals united 
by their edges ; at 
€, are the ten sta- 
mens, nine united 
and one separate ; 
at f, is the pistil, 
the base of which, 
in process of time, 
becomes the pod 
or legume. 
The flowers of the leguminous plants are so pecuhar in appear- 
ance, that they are easily recognised. They are called by botanists, 
irregular. The rose, pink, and bell-flower, are regular in their form ; 
♦hat is, there is a symmetry and equality in their parts. There may 
be shght inequalities in regular corollas; as in the lily we sometimes 
see some petals a Uttle longer than the others ; this is an exception 
to the general rule. It is often owing to a want of discrimination 
between rules and exceptions, that young persons find diflac ulties in 
Class Diadelphia— What two circumstances to be observed with respect to this 
class?— Natural order Papilionacece— l.eguminosae— Describe Fig. 142— Regular co 
rollas. 
Fig. 142. 
