i7S 



CLASS DIADELPHIA. 



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- 

 lionaceoios, 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 falling into error 

 with respect to this class. 



1st. There are some plants with filaments 

 j 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. 



Linneeus, in reference to the form of the flowers, arranged this 

 tribe under a natural order Papilionacea j — Jussieu, regarding the 

 fruit, called the same Leguminosce. 



Papilionaceous Flouc 



Fig. 142 repre- 

 sents the sweet pea 

 {Lathyrns odor a- 

 ins ;) at a, is the 

 five-toothed calyx ; 

 at b, 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 

 c, 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 peculiar in appear- 

 ance, that they are easily recognised. They are called by botanists, 

 irregular. The rose, pink, andbell-llower, are regular in their form ; 

 ^hatls, there is a symmetry and equality in their parts. There may 

 be slight inequalities in regular corollas; as in the lily we sometimes 

 see some petals a little 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 difficulties in 



Class Diadelphia — What two circumstances to be observed with respect to this 

 class?— Natural order Papilionaceae—LeguminosiE— Describe Fig. 142— Regular co 

 rollas. 



Fig. 142, 



