468 PART IV. CLASSIFICATION. 



other plants, belonging to the Naiadacese and other families, re- 

 semble 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. 284 

 A, B, C), but in many cases they appear to be developed from the 

 floral axis (Fig. 284 Z), F, G). However, from careful comparative 

 examination, it seems that the apparently axial ovules may be re- 

 garded in some cases as having been developed on the carpels, their 

 position on the axis being merely the result of a more or less con- 

 siderable 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. 284 (7) is to be found in 

 Butomus, Nymphsea, and Nuphar, the dorsal sutiTre (midrib) of the 

 carpel being the only sterile portion of its internal surface. Of mar- 

 ginal 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 placentas on the wall of the ovary, 

 that is, the placentation is parietal (Fig. 282 S, (7), as in the 

 Violacese, Cruciferse, Papaveracese, Ribesiese, Orchidacese, 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. 282 Z>, and Fig. 284 B) : in 

 a monomerous ovary (Fig. 282 A, and Fig. 284 A) the placentation 

 is essentially parietal, but it is simply termed marginal. 



The position of attachment is a point of descriptive importance, 

 more especially where the number of ovules is small, or where there 

 is but one, in the loculus. When the ovule is attached to the roof 

 so that it down hangs into the loculus, it is said to be pendulous ; 

 when it is attached high up, but at the side, it is suspended 

 (Fig. 284 E) ; when it is attached to the side and projects straight, 

 it is horizontal ; when it is attached at the side, but towards the 

 base and stands up into the loculus, it is ascending. 



When the ovules are borne, either actually or apparently, by the 

 axis, the placentation is said to be axial. When many ovules are 

 borne on the axial placenta (as in the Primulacese, Santalacese, etc., 



