10 PERICARP [CH. I. 



thickness, consistency and even structure, as the fruit 

 ripens, and these alterations commonly invade parts not 

 belonging to the ovary, but fusing with it in the fruit. 

 Consequently the walls of the fruit receive their special 

 terminology, best understood by considering a true fleshy 

 fruit like the plum or cherry. The whole fruit- wall is 

 termed the Pericarp, and this is marked out into three 

 regions an outer thin skin, the Epicarp, an inner bony 

 wall (the stone) or Endocarp, and the fleshy portion 

 between, the Mesocarp. That the stone here is really 

 part of the pericarp is easily shown by the attachment of 

 the seed (kernel) inside, as well as by comparison with 

 very young plums or cherries. The terms 'pericarp ' and 

 its subdivisions are not to be looked upon as strict mor- 

 phological equivalents of particular parts of the ovary- 

 walls : they mark, rather, convenient " geographical " 

 areas, so to speak, and are comparable to such areas as 

 pith, wood, and bark as commonly distinguished in trans- 

 verse sections of stems. They are simply convenient as 

 expressing demarcated regions really visible in such fruits. 



