ORGANS OF EEPRODUCTION. 347 



its being formed upon a common type with the leaf, and that it 

 is consequently homologous with it. 



The carpel being thus shown to be homologous with the leaf, it 

 must necessarily follow that the fruit is likewise a modified con- 

 dition of the leaf, since it is formed of one or more carpels or 

 ovaries, in a matured condition. 



Further proof of the homologous nature of the parts of the 

 flower to the leaf, is afforded by the fact, that the floral axis, 

 instead of producing flowers, will sometimes bear whorls of true 

 leaves. In other cases the axis becomes prolonged beyond the 

 flower, as in certain species of Epacris, and frequently in culti- 

 vated Eoses {fig. 641), &c., or beyond the fruit {fig. 765), and 

 becomes a true branch bearing leaves. To this elongation of the 

 axis the term median prolification is usually applied. 



Various other examples might be adduced of the entire trans- 

 formation 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 condi- 

 tion has also been observed in monstrous Strawberry flowers. 

 In fact, no one can walk into a garden, and examine culti- 

 vated flowers, without flnding numerous instances of transitional 

 states occurring between the different organs of the flower, 

 all of which necessarily go to prove their common origin. 



When a sepal becomes a petal, or a petal a stamen, or a 

 stamen a carpel, the changes which take place are said to 

 be owing to ascending or direct metamorphosis. But when a 

 carpel becomes a stamen, or a stamen a petal, or a 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, and the flower itself to a 

 branch the internodes of which are but slightly developed, so 

 that all its parts are situated in nearly the same plane ; and, as 

 flower-buds are thus analogous to leaf-buds, their parts are also 

 necessarily subject to similar laws of development and arrange- 

 ment, and hence a knowledge of the latter gives the clue to that 

 of the former. 



The symmetrical arrangement of the parts of the flower arising 

 from their being homologous parts with the leaves, will be de- 

 scribed in the next section, together with the various causes 

 which interfere to prevent or disguise it. 



