THE FLOWER. 95 



the superposition of the stamens to the petals in Ehamnacese, the Vine, 

 &c. has been explained by supposing a circle of stamens to have been 

 suppressed between the petals and the existing stamens. Several recent 

 writers attribute the stamens of Rhamnacepe to chorisis of the petals 

 with suppression of the true stamens, extending the same explanation to 

 Ityttnenacese and the Vine, where the true stamens are represented by 

 sterile rudiments or glands within the existing stamens. In the Primrose, 

 according to Pfeffer, the petals originate from the backs of the stamens, 

 though in other cases it would seem that the stamen arises from the petal. 

 In Primulaceae the opposition of the stamens to the petals may, however, 

 be a result of suppression j for in Samolus we find five lobes on the throat 

 of the corolla alternating with the petals, while Lysimachia ciliata has 

 five sterile filaments in addition to five perfect stamens. 



Isomery, Anisomery. Suppression or abortion of part of the 

 organs of one or more circles is, as has been said, a very common 

 cause of want of symmetry. This occurs by far most frequently 

 in the carpellary circles, as might he expected from the organs 

 being crowded on the point of the receptacle (multiplication of 

 carpels occurring, on the other hand, where the receptacle is un- 

 usually developed) ; the stamens exhibit it not unfrequently ; and 

 it is observed also in the petaline whorl, and even in the calyx. 



Symmetrical flowers may be either dimerous, trimerous, tetramerous, 

 or pentanierous throughout ; and when the organs are equal in all the 

 circles the flowers are isomerous, if not so they are anisomerous : thus 

 we have isomerous dimerous flowers in Circcsa (fig. 163) and Syringa 

 (fig. 164), isomerous pentanierous flowers in Crassula (fig. 162), before 



Fig. 163. Fig. 164. Fig. 165. 



Fig. 163. Ground-plan of the 2-merous flower of Circaea: x represents the bract. 



Fig. 164. Ground-plan of the Lilac, with 2-merous circles : x, the bract ; a, a, bracteoles. 



Fig. 165. Ground-plan of a labiate flower, with didynamoua stamens; the posterior one 

 (dotted) suppressed. 



referred to ; but, generally speaking, one or other of the whorls exhibits 

 partial suppression. 



It is rare to find the sepals partially suppressed : perhaps we may con- 

 sider this to be the case as regards the limb of the sepals in such instances 

 as the nappus of Bidens. The corolla exhibits partial suppression in some 

 Leguminosse, where, although the plan of the flowers of the order is 

 pentanierous, in Amorpha only one petal exists ; a transition towards 



