88 THE STRUCTURE OF FLOWERS. 



jDroof for mj theory — that the forms and structures of flowers 

 are the direct outcome of the responsive power of protoplasm 

 to external stimuli.* 



* We may, perhaps, see some analogy between these unions amongst 

 floral organs, which thus occur abnormally in orchids and normally in 

 so many flowers, and inflammatory adhesions in the human subject. 

 It is well known that certain, otherwise abnormal, unions may be con. 

 genital, which usually only occur through inflammation set up by 

 abnormal excitation, but they are not hereditary. 



I have alluded to hypertrophy and atrophy as causes of the struc- 

 tures of flowers, and shall have more to say about them. I would here 

 add the following analogous phenomena between the animal and vege- 

 table kingdoms. Sir James Paget remarks : — " Constant extra-pressure 

 on a part always appears to produce atrophy and absorption ; occasional 

 pressure may, and usually does, produce hypertrophy and thickening. 

 All the thickenings of the cuticle are the consequences of occasional 

 pressure ; as the pressure of shoes in occasional walking, of tools occa- 

 sionally used with the hand, and the like : for it seems a necessary con- 

 dition for hypertrophy, in most parts, that they should enjoy intervals 

 in which their nutrition may go on actively" (Led. on Surg. Path., i. , 

 p. 89). 



The reader will perceive the significance of this passage when 

 recalling the fact that insects' visits are intermittent. 



Atrophy by pressure and absoi'ption is seen in the growth of embryos ; 

 while the constant pressure of a ligature arrests all growth at the 

 constricted place. On the other hand, it would seem to be the persistent 

 contact which causes a climber to thicken (see p. 156). 



