78 THE STRUCTURE OF FLOV/ERS. 



CHAPTER VIII. 



THE PRINCIPLE OF ADHESION. 



Adhesion of Organs. — This term is distinguished from 

 cohesion by limiting its application to the union of different 

 whorls. Thus, if the petals or stamens be united to the 

 calyx, they are called episepalous, a term usually syrony- 

 mous with perigynous ; and if the stamens be adherent to 

 the perianth or corolla, they are epiphyllous or epipetalous 

 respectively, sometimes also described as perigynous. On 

 the other hand, if the stamens and pistil be in close con- 

 junction, showing an adhesion between the filament and the 

 style, so that the anther and stigma are brought together, 

 the term gynandrous is applied to them. 



Adhesion may be safely regarded as an advance upon 

 cohesion; and there is, I think, a great probability of its 

 being — perhaps, originally, in most if not all cases — a result 

 of adaptation to insect agency. 



With regard to the perigynous condition which involves 

 a more or less degree of adhesion of the petals and stamens 

 to the calyx, this is in many clearly a result of the develop- 

 ment of the receptacular tube with its honey-disk lining it, 

 as in Bosacece. This causes the free portions of the petals 

 and stamens to be carried away from the central axis, and 

 placed in a ring "around the pistil," i.e. perigynous; while 

 the more or less amount of adhesion of them to the calyx 



