76 



THE GYNAECIUM 



First Plan of Ovarian Structure. — Two distinct plans for the enclosure 

 of the cavity of the angiospermous ovary are recognized. In the first 

 (Fig. 219) the margins of one carpel meet each other, and then, by more 

 or less of an involution, form the placenta with its two rows of ovules 

 within a single cell. If two or more of such carpels then unite in one 

 compound ovary (Figs. 221 and 222), each necessarily forms its own 

 cavity, and there are as many cells as such a pistil has carpels, unless 

 some modification of structiu'e shall take place, as illustrated below. 



Axillary, Axile, or Central Placentae. — In all cases where closed carpels 

 of this sort unite in a compound ovary, their ventral sides come into 

 contact, and the placentae are brought together at the center and are 

 known as Axillary, Axile, or Central. 



Fig. 219. Transverse section tlirough 1-celled monocarpellary ovary of bean. 220. The same, 

 through 2-celled monocarpellary ovary of Astragalus. 221. The same, through upper 2-celled portion 

 of dicarpellary ovary of Datura. 223. Through lower, 4-chambered portion. 222. The same, through 

 the 5-carpelled and 5-celled ovary of Vaccinium. 224. Through the 5-carpelled, but 10-celled ovary 

 of the flax. 



Abortion of the Septa. — If the septa between the cells now become 

 aborted (Fig. 230), the placentae are left free in the center and are 

 collectively called the Free Placenta. 



True and False Septa and Cells. — ^The walls separating the cells of 

 ovaries constructed upon this first plan, because they consist of the 

 original carpellary walls, are called "True," as are the cells. When, 

 as sometimes happens (Fig. 220), a- new septum develops from the 

 carpellary midrib, extending across to the placenta and separating its 

 two rows of ovules into two cells, the term "False" is applied both to 

 the septum and to the cells so resulting. If there be several carpels to 

 the pistil, and each undergoes this change, it is clear that there must 

 result twice as many cells as there are carpels (Figs. 223 and 224). 



Chambers. — When septa are incomplete, the imperfectly separated 

 cells which result are called Chambers, and the ovary is said to be 

 Chambered. Thus the ovary of Datura is completely 2-celled (Fig. 

 221), but each cell is 2-chambered by partial walls which exist at the 

 basal portion only (Fig. 223). 



