DISPLACEMENT OP PLACENTAS. 99 



and true axile placentation in the same flower in Vinca 

 minor. 



These and many similar changes, which it is not 

 necessary further to allude to, are not so much to be 

 wondered at when it is borne in mind how slight an 

 alteration suffices to produce a change in the mode of 

 placentation, and how frequent is the production of 

 adventitious buds or of foliar outgrowths, as may be 

 seen in the sections relating to those subjects and to 

 Substitutions. 



It will be remembered, also, how, in certain natural 

 orders, under ordinary circumstances, considerable 

 diversity in placentation exists, according as the mar- 

 gins of the carpels are merely valvate or are infolded 

 so as to reach the centre. Often this diversity is due 

 merely to the changes that take place during growth ; 

 thus, the placentation of Cai-yophyllece, Gucurhitacece^ 

 Papaveracece, and many other orders, varies according 

 to the age of the carpel, and if any stasis or arrest of 

 development occurs the placentation becomes altered 

 accordingly. 



It is not necessary, in this place, to enter into the 

 question whether the placenta is, in all cases what- 

 soever, a dependence of the axis, as Payer, Schleiden, 

 and others, have maintained, or whether it be foliar in 

 some cases, axial in others. This question must be 

 decided by the organogenists ; teratologically, how- 

 ever, there can be no doubt that ovules may be formed 

 from both foUar and axial organs, and, moreover, that, 

 owing to the variability above referred to, both in what 

 are called natural and in what are deemed abnormal 

 conditions, it can rarely happen that any safe in- 

 ferences as to the normal or typical placentation of 

 any family of plants can be drawn from exceptional or 

 monstrous formations. 



On the subject of placentation the following authors 

 may be consulted : 



R. Brown, ' Ann. Nat. Hist.,' 1843, vol. xi, 35. Brongniart, ' Ann. Sc. 

 Nat.,' 1834, 86r. 2, i, p. 308. Alph. De Candolle, ' Neue Denkschrift der 



