214 NATURAL HISTORY OF PLANTS. 



error as to their true origin. But this appears to us impossible 

 when the receptacle is cup-shaped as in the Awlworts ;' for then, just 

 as in Rhamnacecs, Rosacea, Leguminosce, &c, the whole inside of the 

 cup is lined by a thin layer which forms a circular rim at the edge, 

 only dilated into four little lobes between the sepals. In the hypo- 

 gynous Greggia the disk is also annular, and simply lobed on the 

 rim. In Selenia, though the flower is tetramerous, it is divided into 

 ten hypogynous lobes. Probably some use might be made in classifi- 

 cation of the characters of the disk, which it is pretty easy to make 

 out in the fresh flower. But from its very origin, 2 it usually be- 

 comes diffluent and indistinct in herbarium flowers softened by 

 soaking : so that no practical use can be made of these characters. 



10. Of the four sepals, the two lateral may or may not be equal 

 in length and breadth to the antero-posterior. They are usually 

 alternative-imbricate in praefloration, rarely valvate or subvalvate, as 

 in Savignga, Ricotia, &c. The greatest dissimilarity in about half the 

 cases usually lies in the insertion. In Brassica, for instance, the 

 insertion of all four sepals is such that their scar on the receptacle 

 forms a moderately curved arc. In Cheiranthus, &c, this is the case 

 with the anterior and posterior only ; the two lateral are inserted 

 along a horseshoe, with more or less divergent branches. Hence 

 at the base of these sepals is a gibbosity, a sac of variable depth, or 

 an obtuse spur, sometimes very prominent like that of Bicentra. 

 This character varies but little within any genus. When the spur 

 is well developed the corresponding gland grows large and projects 

 within its cavity. A rudimentary formation of this kind occurs very 

 rarely in the other sepals. 



11. The petals vary : in the presence or absence of a claw ; in the 

 form of the limb, which may be entire, emarginate, bilobate, or even 

 plurilobate or pinnatifid, as in Brgopetalttm and Schizopetalon ; and in 

 the mode of imbrication in the bud. The corolla is generally regular ; 

 but the anterior petals are much more developed than the posterior 

 in Iberis, which is thus alone distinguished from Tklaspi. Apetalous 

 flowers occur pretty frequently in certain species of Capsella, Coro- 

 nopus, CocMearia, Cardamine, Lepidium, Nasturtium, &c. 



1 See Adansonia, x. 47. of the receptacle, either above or below the 



2 "They only appear very long after the pistil, insertion of the stamens." (Patee, Organog., 

 and are, as Adanson thought, only swollen parts 214.) 



