524 PART III. THE CLASSIFICATION OF PLANTS. 



more rarely it is represented by bands of papillae on tlie ovary 

 itself, when it is said to be pleurogynous. 



The number of the stigmata often affords a means of ascertain- 

 ing whether the ovary is monomerous or polymerous : for instance, 

 the ovary of the Compositse seems, at first sight, to be mono- 

 merous; but the two short branches of the style, each bearing 

 a stigma, show that it is dimerous. On the other band, this 

 character may be misleading : for instance, in various Grasses the 

 ovary bears two or three stigmata, either directly, or springing 

 from the style; hence it might be inferred that the ovary is di- 

 or tri-merous, whilst as a matter of fact it is monomerous. In 

 this respect some few other plants, belonging to the Naiadacese 

 and other families, resemble the Grasses. 



The Macrosporangia or Ovules are always enclosed in the cavity 

 of the ovary, either singly or in larger or smaller number. 

 Usually they may be readily seen to be developed on the carpels 

 (Fig. 338 J-, J5, (7), bul in many cases they appear to be de- 

 veloped from the floral axis (Fig. 338 JD, F, G). However, from 

 careful comparative examination, it seems that the apparently 

 axial ovules may be regarded in some cases as having been de- 

 veloped on the carpels, their position on the axis being merely the 

 result of a more or less considerable subsequent displacement due 

 to the coalescence of the carpels with the axis. That portion of 

 the ovary which bears the ovules is called the placenta. 



The ovules, when borne by the carpels, are but rarely developed 

 over the whole surface of the carpel, but are confined to the margin : 

 in other words the placentation is rarely superficial but generally 

 marginal. Superficial placentation (Fig. 338 C) is to be found in 

 Butomus, Nymphaea, and Nuphar, the dorsal suture (midrib) of 

 the carpel being the only sterile portion of its internal surface. 

 Of marginal placentation there are two varieties : in the one the 

 ovary is syncarpous but unilocular, and the contiguous placental 

 margins of the carpels constitute so many placentae on the wall of 

 the ovary, that is, the placentation is parietal (Fig 336 B, G), as in 

 the Violaceas, Cruciferae, Papaveracea3, E/ibesieae, Orchidaceae, 

 etc. ; in the other the ovary is syncarpous and multilocular, the 

 margins of the carpels meeting in the centre and there bearing the 

 ovules, so that each placenta is at the inner angle of each loculus, 

 that is, the placentation is axile or axillary (Fig. 336 D, and Fig. 

 338 B): in a monomerous ovary (Fig. 336 A, and Fig. 338 A) the 

 placentation is essentially parietal, but it is simply termed marginal. 



