392 GENERAL MORPHOLOGY OF THE FLOWER. 
carpel with the leaf, by tracing its development from a little 
concave body but slightly differing in appearance from a leaf, 
up to its mature condition as a closed cavity, containing one or 
more ovules (see page 268). We have, therefore, as regards the 
carpel, the most conclusive evidence of its being formed upon a 
common type with the leaf, and that it is consequently homo- 
logous with it. 
The carpel being thus shown to be homologous with the leaf, 
it must necessarily follow that the fruit is likewise a modified 
condition of the leaf, since it is formed of 
Fic. 784. one or more carpels in a matured state. 
Further proof of the homologous na- 
ture of the parts of the flower to the leaf 
is afforded by the fact that the floral axis, 
instead of producing flowers, will some- 
times hear whorls of true leaves. In other 
cases the axis becomes prolonged beyond 
the flower, as in certain species of Hpacris, 
and frequently in cultivated Roses (jig. 
655), or beyond the fruit (jig. 784), and 
beconies a true branch bearing leaves. To 
this elongation of the axis the term median 
prolification is usually applied. 
Various other examples might be ad- 
duced of the transformation of the floral 
organs into more or less perfect leaves. 
Thus, in the common White Clover, the 
parts of the flower are not unfrequently 
found in a leaf-like state. A similar con- 
dition has also been observed in monstrous 
Strawberry flowers. In fact, no one can 
walk into a garden, and examine culti- 
vated flowers, without finding numerous 
instances of transitional states occurring 
between the different organs of the flower, 
Fig. 784, A monstrous ®ll of which necessarily go to prove their 
or abnormally devel- common origin. 
oped Pear, showing the When a sepal becomes a petal, or a 
axis prolonged beyond 
the fruit, and bearing petal a stamen, or a stamen a carpel, the 
true or foliage leaves. changes which take place are said to he 
owing to ascending or direct metamorphosis. 
But when a carpel becomes a stamen, or a stamen a petal, ora 
petal a sepal, or if any of these organs become transformed into 
a leaf, this is called retrograde or descending metamorphosis. 
We have thus proved by the most conclusive facts, that all 
the organs of the flower are formed upon a common type with 
the leaf, and differ only in their special development, or, in 
other words, that they are homologous parts. Hence a flower- 
bud is analogous to a leaf-bud, as we have already stated (page 
