292 



THE FLOWER. 



tions or growths from the dorsal suture ; whether in a simple pistil (as 

 that of most species of Astragalus, Fig. 805), or from the back of 

 each proper cell of a compound pistil, as in the Service-berry, the 

 Blueberry, and the common Flax (Fig. 500). 



551. We have considered only the case of compound pistils of two 

 or more cells in the ovary. But compound pistils also not unfre- 

 quently occur 



552. Willi only one Cell. And of these there are two kinds to be 

 noticed, those with axile, and those with parietal placenta. That is, 

 in the first, the ovules are borne in the axis or centre of the ovary, 

 either at the base or on a column which occupies the centre ; in the 

 second, they are borne on some part of the parietes or walls of the 

 ovary. The fii-st, viz. 



553. With a Free Central Placenta, is found in the Primrose, Purslane 

 50, (Fig. 389), and Pink families (Fig. 432, 501, 502). 



In the Pink family this evidently results from the ob- 

 literation of the dissepiments (as many as there are 

 styles or stigmas) ; and vestiges of these may be de- 

 tected at an early stage, and sometimes at the base of 

 the full-grown ovary ; while certain plants of the same 

 family, of otherwise identical structure, retain the par- 

 titions even in the ripe pod. In other instances, as in 

 Dionsa, Thrift, &e., this is doubtless a modification of 

 parietal placentation, with ovules produced only at the 

 bottom. This brings us to the case of compound one- 

 celled pistils 



554. Willi Parietal Placenta), that is, with the placentas borne on 

 the sides or parie- 

 tes of the ovary, 

 as in the Poppy, 

 Caper, Cistus or 

 Rock-Eose (Fig. 

 507), Violet, Sun- 

 dew (Fig. 510), 

 and Currant families, and many others. To comprehend tliis per- 



FIG. 501. Vertical section through the compound tricarpellary ovary of a plant of Spergu- 

 laria rubra, showing the free central placenta. 502. Transverse section of the same. 



FIG. 503-505. Diagrams illustrating parietal and free central placentation. 503. Cross- 

 section of a tricarpellary ovary, with a free central placenta, produced by the obliteration of 

 the dissepiments. 504. Section of an ovary with three strictly parietal placeat£e. 505. Same, 

 except that there are incomplete partitions. 



