288 



ORGANOGRAPHY. 



satisfactorily explained by considering the placenta as a produc- 

 tion of the axis. 



In a practical point of vie^V•, the mode of production of the 

 placenta is of little importance. The accurate discrimination of 

 the different kinds is however of much value in descriptive botany, 

 by affording us constant, and hence important characters, for dis- 

 tinguishing plants. Some natural orders exhibit more than 

 one kind of placentation, and hence cannot be distinguished by 

 any particular one ; in such orders, therefore, the placentation 

 can only be applied in obtaining good characteristics of certain 

 genera. In the majority of instances, however, we find one kind 

 of placentation occurring throughout all the plants of a particu- 

 lar natural order. Thus, the Scrophulariaceae, Ericaceae, Cam- 

 panulacea?, &c., present us Avith axile placentation ; the Papave- 

 racew, Violacere, Grossulariaceae, Orobanchaceae, Cruciferis, &c., 

 with parietal ; and the Caryophyllacere, Santalace^, Primulaceae, 

 &c., with free central. 



2. The Style. — We have already described the genei-al nature 

 and structure of the style in speaking of the cai-pel. There 

 are certain other matters connected with it still to be alluded 

 to. 



The style generally arises from the geometrical summit of 

 the ovary, of which it is a continuation in an upward direction, 

 as in the Primrose {fig. 567), it is then termed apicilar or 

 apical. In other cases, the apex of the ovary becomes inflected 

 towards the side or base, from the carpel or carpels of which it 

 is formed being folded like ordinary leaves in reclinate vernation, 

 the style then becomes /afera/, as in the Strawberry (fig. 623), 

 or basilar, as in the Alchemilla (fig. 624). In the two latter 



Fig. 623. 



Fig. 624. 



Fig. 625. 



Fig. 02.3. One of tl\e carpels of the Strawberry with a lateral style ^V;. 



«2». Carpel of Alclmnilhi with a basilar style- The stigma is capitate. 

 Fig. C25. Vertical Kcctioii of the ovary of Bubingtunia. From Lindiey. 



cases tlicrcforc, tlic geometrical and organic apices of the ovary 

 do not con-csi)ond, as the point of origin of the istylc always de- 

 termines the latter. 



