120 



THE PrSTILS. 



[LESSON 18. 



318. With a FrCC Central Placenta, is what we find in Purslane 

 (Fig. 2 1-1), and in most duckweeds (Fig. 258, 259) and Pinks. 

 The difference between this and the foregoing case is only that the 

 delicate partitions have very early vanished ; and traces of them 

 may often be detected. Or sometimes this is a variation 

 of the mode 



319. With Parietal Placenta 1 , namely, with the ovules 

 and seeds borne on the sides or wall (parietes) of the 

 ovary. The pistil of the Prickly Poppy, Bloodroot, 

 Violet, Frost-weed (Fig. 2G1), Gooseberry, and of 

 many Hypericums, are of this sort. To understand it 

 perfectly, we have only to imagine two, three, or any 

 number of carpel-leaves (like that of Fig. 

 251), arranged in a circle, to unite by their 

 contiguous edges, and so form one ovary 

 or pod (as we have endeavored to show in Fig. 260) ; 

 very much as in the Stramonium (Fig. 199) the 

 five petals unite by their edges to compose a mono- 

 petalous corolla, and the five sepals to form a tubular 

 calyx. Here each carpel is an open leaf, or partly 

 open, bearing ovules along its margins ; and each 

 placenta consists of the contiguous margins of two 

 pistil-leaves grown together. 



320. All degrees occur between this and the sev- 

 eral-celled ovary with the placentas in the axis. Com- 

 pare, for illustration, the common St. John's-worts, Fig. 255 and 256, 

 with Fig. 262, a cross-section of the ovary of a different species, in 

 which the three large placenta} meet in the axis, but 

 scarcely unite, and with Fig. 263, a similar section of 

 tin- ripe pod of the same plant, showing three parietal 

 plari'iitse borne on imperfect partitions projecting a 

 lit lit; way into the general cell. Fig. 261 is the same 

 in i lan, but with hardly any trace of partitions ; that 

 is, the united edges of the leaves only slightly project into the cell. 



IMC. 2M. Pistil of a Sandwort, with the ovary divided lengthwise; and 259, the same 



i Hy, in show the free central placenta 



PlM of a (.111- celled (.vary of throe carpel-leaves, with parietal placenta?, cut 

 !'>u , u here it is complete ; the upper part showing the top of the three leaves it is 

 "I- :|'l'r<>r-ljiii K , lint not united. 



1 "' ' of the ovary of Frost-weed (Hehautheiauni), with three parietal 



placviiut. Woariii" ovule*. 



