CHAP. II. 
OVARY. 
169 
considerations : viz., that, as the carpels are modified leaves, 
they are necessarily subject to the same laws of arrangement, 
and to no others, as leaves developed around a common axis 
upon one or several planes. For no axiom appears more in- 
contestable in botany, than that all modifications of a given 
organ are controlled essentially in the same way, and by the 
same influences, as the organ itself in an unmodified state : 
and hence every theory of the structure of fruit which is not 
reducible to that which would be applicable to the structure 
of whorls of leaves is vicious of necessity. I shall proceed to 
demonstrate the perfect accordance of the carpellary theory 
of structure in every point with these principles. 
The placenta arises from the two margins, either distinct 
or more usually combined, of a leaf folded inwards. When 
a leaf is folded inwards, its margins will point towards the 
stem or axis around which it is developed ; and in a whorl 
of leaves such inflected margins would all be collected 
round a common centre ; or, if the axis were imaginary, 
in consequence of the whorl being terminal, would be 
placed next each other, in a circle of which the back of the 
leaves would represent the circumference. Therefore the 
placentae will always be turned towards the axis, or will 
actually meet there, forming a common centre ; and, which 
is a very important consequence of this law, if one carpel 
only, with its single placenta, be formed in a flower, the true 
centre of that flower will be indicated by the side of the car- 
pel occupied by the placenta. Proofs of this may be found 
in every blossom: but particularly in such as, habitually 
having but one carpel, occasionally form two, as the Wisteria 
sinensis, Alchemilla arvensis, Cerasus acida, &c. ; in these the 
second carpel, when added, does not arise by the side of the 
first, but opposite to it, the face of its placenta being in fi'ont 
of that of the habitual carpel. A fourth proof of this uniform 
direction of the placentae towards the axis is afforded by 
those pistils in which a great number of carpels is developed 
in several rows, as in the Strawberry and the Ranunculus : 
in all these the placentae will be, without exception, found 
directed towards the axis, and consequently towards the 
