SECTION 10.] 



PISTILS. 



107 



the midrib of the leaf, not a seam therefore ; but at maturity many fruits, 

 such as pea-pods, open by this dorsal as well as by the ventral line. 



PLACENTA, a name given to the surface, whatever it be, which bears 

 the ovules and seeds. The name may be needless when the ovules grow 

 directly on the ventral suture, or from its top or bottom ; but when there 

 are many ovules there is usually some expansion of an ovule-bearing 

 or seed-bearing surface; as is seen in our Mandrake or Podophyllum, 

 Fig. 326. 



309. A Compound Pistil is a combination of two, three, or a greater 

 number of pistil-leaves or carpels in a circle, united into one body, at least 



326 327 328 329 330 



by their ovaries. The annexed figures should make it clear. A series 

 of Saxifrages might be selected the gyiicecium of which would show every 

 gradation between two simple pistils, or separate carpels, and their com- 

 plete coalescence into one compound and two-celled ovary. Even when 

 the constituent styles and stigmas are completely coalescent into one, the 

 nature of the combination is usually revealed by some external lines or 

 grooves, or (as in Fig. 328-330) by the internal partitions, or the number 

 of the placentae. The simplest case of compound pistil is that 



310. With two or more Cells and Axile Placentae, namely, with as 

 many cells as there are carpels, that "have united to compose the organ. 



FIG. 326. Simple pistil of Podophyllum, cut across, showing ovules borne on 

 placenta. 



FIG. 327. Pistil of a Saxifrage, of two simple carpels or pistil-leaves, united at 

 the base only, cut across both above and below. 



FIG. 328. Compound 3-carpellary pistil of common St. John's-wort, cut across : 

 the three styles separate. 



FIG. 329. The same of shrubby St. John's-wort ; the three styles as well as 

 ovaries here united into one. 



FIG. 330. Compound 3-carpellary pistil of Tradescantia or Spiderwort ; the three 

 stigmas as well as styles and ovary completely coalescent into one. 



