BASAL AND APICAL PLACENTAE 



77 



Second Plan of Structure. — Quite a different group of appearances 

 will result from the higher or more complex form of carpel union, by 

 which the proximate margins of two adjacent carpels meet and unite 

 (Fig. 225) instead of two belonging to the same carpel. The result of 

 this form must be a single cavity or a 1-celled ovary, without regard 

 to the number of carpels, unless, as in the mustard (Fig. 226), one or 

 more false septa may divide it. 



Axillary Placentae. — It has been observed that in all cases of the 

 first plan of ovarian structure, the placentae will be central. It is 

 equally clear that in all cases of the second, the placentae must be 

 formed upon the sides, where the edges of the carpels meet. Such 

 placentae are called Parietal (Figs. 225 to 229). Such placentae may, 

 by an extensive involution of the margins, be carried very nearly, or 

 quite, to the axis (Figs. 227 and 228), but unless cohesion actually 

 occurs at that point they are parietal and the ovary is 1-celled. 



226 



230 



Fig. 225. The 2-carpelled, l-celled ovary of the gentian. 226. 2-carpeIled and falsely 2-celled ovary 

 of mustard. 227. A 2-carpeIled, 1-ceIled ovary, its placentae nearly meeting in the axis. 228 and 229. 

 The same, 3-carpelled. 230. The free central placenta of Primula. 231. A 1-celled ovary with basal 

 placenta. 232. 2-carpelled, 1-celled ovary of Oholaria, the placentae extended to completely line the 

 wall. 



Modifications of the Placenta. — Some further modifications of the 

 placenta require our consideration. The free central placenta has 

 been considered. Such a placenta frequently becomes partly aborted 

 by the gradual disappearance of its upper portion. 



Basal and Apical Placentae. — This process may continue until the 

 placenta is reduced to a trace at the base (Fig. 231). In other cases it 

 will be reduced to a trace at the apex (Figs. 235 and 237). Basal or 

 apical placentae may be Centric or Eccentric. Modifications of these 

 processes may result in restricting the placenta to any intermediate 

 point. Upon the other hand, such a placenta may become enlarged and 

 fleshy. Similar changes may occur in the parietal placenta. It may 

 become reduced to a mere point preserved at the apex, base, or inter- 

 mediate portion. In the watermelon it becomes enormously enlarged. 



