APPENDIX E. 



THE SHAPES AND ARRANGEMENTS OF FLOWERS. 



In Part IV., Chapter X., under the title of " The Shapes of 

 Flowers," I have, after describing their several kinds of symmetry, 

 as habitually related to their positions, made some remarks by way 

 of interpretation. The truth that flowers exhibit a radial symmetry 

 when they are so placed as to be equally affected all round by 

 incident forces, having been exemplified, and also the truth that 

 they assume a bilateral symmetry when they are so placed that 

 their two sides are conditioned in ways different from the ways in 

 which their upper and lower parts are conditioned ; I have gone 

 on to inquire (in § 234) by what causes such modifications of 

 form are produced. I have stated that, originally, I inclined to 

 ascribe them entirely to differences in the relations of the parts 

 to physical forces — light, heat, gravitation, etc. ; but that I found 

 sundry facts stood in the way of this interpretation. And I have 

 said that " Mr. Darwin's investigations into the fertilization of 

 Orchids led me to take into account an unnoticed agency." Con- 

 tinuing to recognize the physical forces as factors having some 

 influence, I have concluded that the most important factor is the 

 action of insects ; which, aiding most the fertilization of those 

 flowers which most facilitate their entrance, produce, in course of 

 generations, a form of flower specially adapted to the special 

 position. 



Though still adhering to this interpretation, I have since found 

 reason to think that the original interpretation contains a larger 

 portion of truth than I supposed at the time when I was led thus to 

 revise it. While staying at Miirren, in Switzerland, in 1872, 1 ob- 

 served some modifications in a species of Gentian, which proved to me 

 that the action of incident physical forces on flowers is, in some cases, 

 very rapid and decided. The species furnishing this evidence was the 

 Gentiana Asclepiadea ; which If ound in a copse formed of bushes that 

 were here wide apart and there close together. In some places not 

 near to the bushes, the individuals of the species grew vertically ; in 

 other places, partially shaded, their inclined shoots curved in such 

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