120 



THE riSTILS. 



[m:sson 18. 



318. With* a Free Ccillral I'laCCIlta. is uhat we find in Purslane 

 (Fig. 214), ami in most Ciiickweeds (Fig. 2.38, 2.J'j) and Pinks. 

 The diffcreuce between this and the foregoing case is oidy that the 

 delicate partitions have very early vanished ; and traces of thera 

 may often be detected. Or sometimes this is a variation 

 of the mode 



319. With rarictal Placenta:, namely, with the ovules 

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

 o%ary. The i)istil 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 eaeli carpel is an o|)en 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 placentre in the axis. Com- 

 pare, for illustration, the common St. John's-worts, Fig. 2oa and '2')Q, 

 with Fig. 2G2, 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. 2G3, a similar section of V^^^^<^ 

 the ripe pod of the same plant, showing three parietal 

 placenta} borne on imperfect partitions projecting a 

 little way into the general cell. Fig. 2G1 is the same 

 in plan, but with hardly any trace of partitions ; that 

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



FIG. 25S. Pistil of a Sandwort, with the ovarj' divided lengthwise; and 259, tlio same 

 divided transversely, to show tlie free central placenta 



FIG. SCO. Plan of a one-celled ovary of three carpel-leaves, with parietal iilareiita>, rut 

 across below, where it is complete; the upper p:iit showing the tup of the Ihroc Icives it la 

 com|M>sed of, approacliinji, hut not united. 



FIG. 2r,l Cross-se<'tioii of the ovary of I'rost-weed (llcliaulhemuui), w ith three parietal 

 {ilaccntw^ bearing ovules. 



