200 
ORGANOGRAPHY. 
BOOK I. 
Goethe lias well remarked, in the genus Nigella, in which N. 
orientalis has the carpels partially united, while N. damascena 
has them completely so ; in the latter case, however, the styles 
are distinct. They and the stigmas are all consolidated in a 
single body, when the pistil acquires its most complete state 
of complication, as in the Tulip ; which is, however, if care- 
fully examined, nothing but an obvious modification of such 
a pistil as that of Nigella damascena. 
This important conclusion is deducible from the foregoing 
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 stat^ : 
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 usually arises from the two margins, either 
distinct or 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 conse- 
quence 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 carpel 
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 Wistaria 
sinensis, Alchemilla arvensis, Cerasus acida, &c.; in these the 
