XXXIV MODIFICATIONS OF FLOWER 473 



There are one or two important modifications of the 

 flower which must be briefly referred to. 



In the Christmas-rose {Helleborus) the general structure 

 of the flower resembles that of the buttercup except that the 

 petals (Fig. 127, a^, pt) are small and tubular, and the 

 sepals (sp) so large as to form the obvious and attractive 

 part of the flower. But the large carpels {cp) are few — three 

 to six — in number, arranged in a single whorl, and closely 

 applied to one another by their lateral faces (a^). The 

 peripheral or outwardly-facing border of each represents the 

 midrib (inr) of the carpellary leaf, the central border— that 

 facing the axis of the flower— its united edges {e). To the 

 latter are attached several megasporangia arranged in a 

 longitudinal row. 



In the Canterbury-bell {Campanula) there appears at first 

 sight to be a single carpel (b^ vnt) with three stigmas {stg). 

 But a transverse section of the venter (b^) shows it to 

 contain three cavities arranged round a longitudinal axis to 

 which are attached three rows of ovules (nig. spg), one to 

 each chamber. Obviously such a pistil is produced by the 

 three carpels of which it is composed being not simply 

 applied to one another as in the Christmas-rose, but actually 

 fused. In the currant {Ribes) the pistil shows in transverse 

 section a single cavity only (c), but with two rows of ovules 

 {mg. spg) : here the carpellary leaves have united with one 

 another simply by their edges. 



Campanula illustrates concrescence not of the carpels 

 only but of all the other floral whorls. The sepals have 

 united to form a cup-like calyx (Fig. 127, b\ cat), the petals 

 are joined into a vase-like corolla {cor), and the filaments of 

 the stamens {fl) are united below. Moreover, the floral 

 receptacle {fl. r) instead of being conical, as in the butter- 

 cup, is hollowed into a cup which encloses and is fused with 



