294 THE FLOWEK. 



and a single style. A pistil of two carpels may be two-celled, with 

 two placentre, two styles, or two stigmas, &c.* 



* There are, however, some exceptions which qualify these statements : — 



1. Each placenta being a double organ (556), it occasionally happens that, 

 the two portions are separated more or less, as in Orobanchaceous plants, where 

 a dicarpcUary ovary appears on this account to have four parietal placentae ; 

 either approximate in pairs (as in our Cancer-root, Conopholis), or equidis- 

 tant (as in Aphyllon). 



2. Analogous to this is the case where the two constituent elements of the 

 stigma (the only essential part of the style) separate into two half-stigmas, as is 

 partially seen in Fig. 494, 495. The stigma, no less than the placenta, belongs 



to the margins of the infolded leaf (545), these margins being 

 ovidiferouf in the ovary and stigmaiiferous in the style ; as Mr. 

 Brown, the most profound botanist of this or any age, has 

 clearly shown. These two constituent portions of the style or 

 stigma occasionally separate, either entirely or in part, as in 

 Euphorbiaceous plants, in Grasses, and especially in Drosera 

 (Fig. 510), where there are consequently twice as many nearly 

 distinct styles as there are parietal plaeentje in the compound 

 ovary If the two component parts of the style of each carpel 

 were reunited into one, in the usual manner, their number 

 would equal the placenta, and their position would bo alter- 

 nate with the latter. But since, in parietal placentation, each 

 ^'^ half-placenta is confluent (not with its fellow of the same 



carpel, but) with the contiguous half-placenta of the adjacent carpel, it were surely 

 no greater anomaly for the elements of such half-stigmas as those of Rrosera to 

 follow the same course. This is precisely what takes place in Parnassia, and in 

 other cases where the stigmas are opposite the parietal placentje ; — cases which 

 were thought to be very anomalous, merely on account of the adoption of a 

 false principle (that of the necessary alternation of the stigmas and placentie), 

 but which are really no more extraordinary than parietal placentation itself 



3. Furthermore, the production of ovules is not always restricted to what 

 answers to the margins of the carpellary leaves. In the Poppy, the whole sur- 

 face of the long, imperfect partitions is covered with ovules ; in Butomus, they 

 are borne over the whole internal face of each cai-pel, and in Water-Lilies over 

 the whole surface, except the inner angle of each cell, where alone tliey normally 

 belong. Reduced to two in the allied "Water- Shield (Brasenia, Fig. 684), the 

 ovules grow from the dorsal suture, or the midrib of the carpellary leaf alone ! 

 And in the allied Cabomba itself we usually find its three ovules, one'bn the 

 dorsal and one on the ventral suture, and the third on some variable part of tlie 

 face of the cell in the vicinity of either suture. In Obolaria, Bartonia (Cenfau- 

 rella, Michx.), and in several species of Gentian, a compound one-celled ovary is 

 ovuliferous over the whole face of the cell ! 



All placentation is very differently explained by those who adopt the hypoth- 



FIG. 510. Pistil of Drosera filiformis, ■with three deeply two-pai-ted styles : the ovary cut 

 across, showing three parietal placeutfe. 



