BASAL A^'D APICAL PLACENTAE 



77 



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

 will result from the liiii^lier or more comi)lex form of carpel union, by 

 which the ])roximate 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. 22(1), 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 p(Mnt they are parietal and the ovary is 1-celled. 



;i>26 



230. 



Fig. 225. The 2-carpeIled, 1-celled ovary of the gentian. 22G. 2-carpelled and falsely 2-celled ovary 

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

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

 placenta. 232. 2-carpclIed, 1-celIed ovary of Ubolaria, 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 (lisai)])earaiice of its upper portion. 



Basal and Apical Placentae. — Tliis 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 Fccentric. Modifications of these 

 processes may result in restricting the placenta to any intermediate 

 point. Upon the other hand, such a j)lacenta may become enlarged and 

 fleshy. Similar changes may occur in the j)arietal placenta. It may 

 become reduced to a mere point pre.ser\e(l at the apex, base, or inter- 

 mediate portion. In the watermelon it becomes enormously enlarged. 



