9 8 



BOTANY. 



it gives clear ideas of the varied and complex characters 

 of ovaries ; and these characters are of the greatest value 

 in classification. 



EXERCISE XLIII. 

 Placentation. 



After studying the structure of ovaries, as explained 

 in Ex. XLII, the following definitions will be easily un- 

 derstood : 



PLACENTATION. The arrangement of placentas is 

 called placentation. 



To determine the mode of placentation of a plant, 

 slice its ovary across, and compare its appearance with the 



FIG. 291. 



FIG. 292. 



FIG. 293. 



FIG. 294. 



following figures. The formation and arrangement of pla- 

 centae are so various, that we have given an unusual num- 

 ber of drawings to illustrate the definitions. 



FIG. 296. 

 FIG. 295. 



AXILLARY PLACENTATION. When the ovules are 

 found along the central line, or axis of the pistil, the pla- 



