ORGANS OF REPRODUCTION. 



283 



line or ridsre which is formed by the union of several placentas. 

 These placentas are variously distributed in different plants, but 

 tlieir arrangement is always the same for any particular one, 

 •whence their accurate discrimination is of veiy great import- 

 ance. The term placentation is used to indicate the manner in 

 whicli the placentas are distributed. The placenta is called by 

 Schleiden the spermophore. 



In describing tliis subject, we shall first allude to the different 

 kinds of placentation, and then proceed to explain the views 

 generally entertained as to their origin. 



I. Kinds of Placentation. — In the simple ovary, the placen- 

 ta is situated at the p-^ gl3^ 

 ventral suture or that 

 point which coiTesponds 

 to the union of the two 

 margins of the carpel- 

 laryleaf(y?f7.61.3) ; such 

 a placenta is therefore 

 termed marginal, or axile 

 from its being turned 

 towards the axis of the 

 plant. 



In compound ovaries 

 we have three different 

 kinds of placentation ; 

 namely, axile, parietal, and free central. The axile occurs in 

 all compound many-celled ovaries, because in these each of the 

 component carpels is placed in a similar position to the simple 

 OA-ary, and hence the placentas situated at their ventral sutures 

 will be arranged in the centre or axis, as in the Lily {fig. 614), 

 and Campanula {fig. 615). By many botanists this mode of 



Fig. fil3. Vertical section of the flower of 

 the Stonecrop. pi. Placenta of one of the 

 carpels arising from llie ventral suture. 



Fig. 614 



Fig. 616. 



Fig. 614. Transverse section of the compound ovary of the Lily. The ovary 



is trilocular. The placentas, 7)/, are axile Fig. CA^. Transverse section 



of the ovary of Campanula. The ovary is five-celled, and tlie placentation 



^?, axile. Fig.iWCi. Transverse section of tlie ovary of a Cactus. The 



ovary is unilocular and the placentation parietal. 



