CHAPTER XXVIII. 



PROGRESSIVE METAMORPHOSES. 



Homology. — The theory of homology has long been main- 

 tained, and has met with such an overwhelming mass of 

 evidence in its favour, that it is now regarded as a well- 

 established morphological doctrine. The belief that every 

 individual member of a flower, whether sepal, petal, stamen, 

 or carpel, may be interchangeable with a leaf, and that they 

 are therefore all phyllomes or foliar appendages to the axis, 

 scarcely requires proof. Secondly, any one organ may 

 theoretically be substituted for any other, so that although a 

 sufficient number of interchanges has not yet been met with 

 to make a complete series of permutations, yet they have 

 gone far towards strengthening the probability that such 

 might be possible.* 



I propose giving a very abbreviated series to illustrate, 

 first, progressive changes from leaves through bracts to 



* The metamorphosis, with the exception of the substitution of 

 petals for other organs, is rarely more than tentative ; for it is, as it 

 were, a mere attempt to effect a change, so that wherever a " monstrous" 

 organ bears ovules they are almost always rudimentary and quite 

 incapable of being fertilised. I have said "rarely," for M. Brongniart 

 succeeded in obtaining fertile seeds from artificial impregnation of 

 ovuliferous stamens in Polemonium coeruleum (Bull. Soc. de Bot. Fr.y t» 

 viii., p. 453). 



