DISPLACEMENT OF 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 shght an 
alteration suffices to produce a change in the mode of 
placentation, and how frequent is the production of 
adventitious buds or of folhar 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 Caryophyllee, Cucurbitacee, 
Papaveracee, 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 fohar 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 : 
RB. . Brown, ‘ Ann. Nat. Hist.,’ 1843, vol. xi, 35. Brongniart, ‘Ann. Sc. 
Nat.,’ 1834, sér. 2, i, p. 308. Alph. De Candolle, ‘Neue Denkschrift der 
