224 



FLOWERS AND THEIR WORK. 



Fig. 75. Diagram of Syncarpous Ova,\-y, with 

 Parietal Placentation. 



syncarpous pistil. The union may be confined to the base of the ovary 

 (some Saxifrages), or may include the entire ovary (Campion), or only 

 the stigmas may be free (Foxglove), or all three may be completely 



united together (Primrose). 

 A syncarpous ovary may be 

 divided into a number of cham- 

 bers, each corresponding to the 

 cavity of one carpel. Thus 

 the Tulip has three carpels, 

 and the ovary is divided into 

 three chambers, each contain- 

 ing a double row of ovules. 



The ovary of the Violet has 

 a single chamber only, although 

 it is composed of three carpels, 

 as is indicated by the presence of three groups of ovules arranged 

 in longitudinal rows upon its wall. When, as in this case, the ovules 

 are attached to the wall of a compound ovary, the placenta- 

 tion, or arrangement of the placentas, is said to be parietal (Fig. 

 75) ; but when the ovules arise from the longitudinal axis in the 

 centre of the ovary, the placentation is said to be axile (Fig. 76), 

 e.g. Bluebell, Tulip. It will be noticed that when the placentation 

 is axile, the ovules in each loculus are derived from the margins of 

 the carpellary leaf that forms this chamber, whereas in the case of 

 parietal placentation each group of ovules is derived from the margins 

 of two adjacent carpellary 

 leaves, half from each. In 

 Chickweed, Stitchwort, Cam- 

 pions, Primrose, etc., the cen- 

 tral axis of the ovary does not 

 reach the roof of the latter, so 

 that the ovules appear to arise 

 from a mound in the centre 

 of the ovary ; this type of 

 placentation is said to be free- 

 central. 



The number of chambers in 



an ovary usually corresponds, if there are more than one, to the 

 number of carpels of which it is composed. In Labiates and Borages, 

 however, each compartment of the bicarpellary gynecium is divided 

 into two, so that there are four loculi, but only two carpels. The ripe 

 ovary of the Flax becomes similarly divided into ten chambers instead 

 of the five present at first. 



Again, in unilocular ovaries with parietal placentation, each placenta 

 usually corresponds to a single carpel. The number of styles or 

 stigmas often corresponds to the number of component carpels, and 

 the ripe fruit frequently splits into as many pieces as there are carpels. 

 In White Water-lily the numerous petals pass by gradual transitions 

 into the more centrally placed stamens, all being spirally arranged on 

 the receptacle ; in double Roses the stamens, in double Buttercups 



Fig. 76. Diagram of Syncarpous Ovary, with 

 Axile Placentation. 



