POLTOAMIA. 433 



tain instance of this, except H'lppophae, 

 already mentioned under Monotcia Te- 

 tramh'ia. 



3. Trioecia. Of the only two genera which 

 have ever been placed here, Ceratonia, 

 Cavcnu Ic. t. 113, belongs to Ptmtandrla 

 Moiioiiynia. Ficiis is so celebrated for the 

 diversity of its flowers, as connected with 

 the history of vegetable impregnation, see 

 p. 336, that we are glad to take advantage 

 of a tritiini>: ditference in the calyx of the 

 two florets, (the barren one being most fre- 

 quently three-cleft, the fertile five^cleft,) 

 to keep it here. 



All things being considered, this Class 

 may be thought scarcely worth retaining. 

 Yet as we know two or three genera entitled 

 to a place in it, upon principles which the 

 analogy of the two preceding Classes shows 

 to be sound, we cannot tell but others may 

 exist in the unexplored parts of the globe. 

 For this reason, and for the uniformity of 

 the system, I would venture to preserve it. 

 If the 21st and 22d Classes should hereafter 

 be reformed by some judicious and experi- 



