118 



THE PISTILS. 



[LESSON 18. 



cavity of the ovary, and bears the ovules, is called the Placenta* 

 Obviously a simple pistil can have but one placenta ; but this is in 

 its nature double, one half answering to each margin of the leaf. 

 And if the ovules or seeds are at all numerous, they will be found 

 to occupy two rows, one for each margin, as we see in Fig. 252, 172, 

 in the Marsh-Marigold, in a Pea-pod, and the like. 



309. A simple pistil obviously can have but one cavity or cell; 

 except from some condition out of the natural order of things. But 

 the converse does not hold true : all pistils of a single cell are not 

 simple. Many compound pistils are one-celled. 



310. A simple pistil necessarily has but one style. Its stigma, 

 however, may be double, like the placenta, and for the same reason 

 (305) ; and it often exhibits two lines or crests, as in Fig. 252, or it 

 may even be split into two lobes. 



311. The Compound Pistil consists of two, three, or any greater 



number of pistil-leaves, 

 or carpels (305), in a 

 circle, united into one 

 body, at least by their 

 ovaries. The Culti- 

 vated Flax, for exam- 

 ple (Fig. 212). has a 

 compound pistil com- 

 posed of five simple 

 ones with their ovaries 

 united, while the five 

 styles are separate. 

 But in. one of our 

 wild species of Flax, the styles are united into one also, for about 

 half their length. So the Common St. John's wort of the fields has 

 e compound ovary, of three united carpels, but the three styles are 

 separate (Fijr. 2-").")), while some of our wild, shrubby species have the 

 Styles al^o combined into one (Fig. 256), although in the fruit they 

 often split into three a;ain. F,ven the ovaries may only partially 

 combine with each other, as we see in different species of Saxifrage, 

 eome having their two pistils nearly separate, while in others they 



FIG. 254. Pistil of a Saxifrapr, of two simple carpels or pistil-leaves, united at the base 

 inly, cut across both above and below. 



FIG. 255. Compound pistil of common St. John's-wort, cut across : styles separate. 

 FIG. 256. The same of shrubby St. John's-wort ; the three styles united into one- 



