ORGANS OF BEPKODUCTION. 275 



either perfectly smooth, or furnished in various ways with dif- 

 ferent kinds of hairs, or prickles ; or it may assume a glandular 

 appearance ; in which cases the same terms 

 are used as in describing similar conditions of Fig. 613. 

 the surface of the leaves, or of the other organs 

 of the plant. 



When the ovary is compound, the number 

 of carpels of which it is composed may be 

 ascertained in one or more of the following 

 ways. Thus, when the styles or stigmas re- 

 main distinct, the number of these generally 

 corresponds to the number of carpels. It 

 does, however, occasionally happen, as in Eu- 

 phorbia {fig. 613), that the styles are them- Fig. eis. Pistillate 

 selves divided, in which case they would S^of^^wpft^ 

 of course indicate a greater number of carpels «>*«. with three 

 than are actually present ; we must then re- ^^^^^ styles. 

 sort to other modes of ascertaining this point, such, for instance, 

 as the furrows, or lobes on the external surface of the ovary, or 

 the number of partitions or loculi which it contains, as these 

 commonly correspond in number to the carpels of which that 

 ovary is composed. The mode of venation may in some cases 

 also form a guide in the determination ; while in others the 

 manner in which the ovules are attached must be taken into 

 consideration. We will now pass to the examination of the 

 latter point. 



Placentation. — The term placenta is commonly applied to the 

 more or less marked projection occurring in the cavity of the ovary 

 to which the ovules are attached. The placentas are variously 

 distributed in different plants, but their arrangement is always 

 the same for any particular species, whence their accurate dis- 

 crimination is of great importance. The term 'placentation is 

 used to indicate the manner in which the placentas are distri- 

 buted. The placenta is called by Schleiden the spermophore. 



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

 kinds of placentation, and then proceed to explain the views 

 generally entertained as to their origin. 



1. Kinds of Place7itation. — In the simple ovary the placenta 

 is always situated at the ventral suture or that point which cor- 

 responds to the union of the two margins of the lamina of the 

 carpellary leaf (fig. 614), out of which it is formed ; such a pla- 

 centa is therefore termed marginal, or sometimes axile from its 

 being turned towards the axis of the plant. The latter term is 

 better reserved for the placentation of compound ovaries, as 

 described below. 



In compound ovaries we have three kinds of placentation ; 

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

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

 T 2 



