398 



ROSACEA 



Eventually the single carpel which is left develops into a 

 drupe (the fruit) {£, Fig. 1 24). The ovary wall (/) increases in 

 thickness, and when ripe exhibits three layers of tissue of different 

 texture, viz. : (i) an inner, hard, bony layer (e) next the seed 

 termed the ' stone ' of the fruit or endocarp, consisting of scleren- 

 chymatous cells ; (2)3- soft parenchymatous layer (in) — the 

 ' flesh ' or mesocarp — with sweet cell-sap ; and (3) an outer 

 thin skin or epicarp. 



During the early growth, increase in size of the fruit proceeds 



Fig. 124. — A, Vertical section of the flower of a plum, x Receptacle; o petal; a 

 stamens ; p ovary, inside which is seen an ovule. The part of the receptacle ahove the 

 XvMifx falls off after fertilisation. 



B^ Fruit (drupe) developed from the gyngecium of the flower A, / The pericarp, of which 

 e is the endocarp or ' stone ' ; ?;z the mesocarp or ' flesh ' ; s seed ; si point where style 

 has fallen ofif ; x small remaining part of the receptacle. 



rapidly up to what is known as the ' stoning period ' when the 

 endocarp is beginning to harden, at which time growth in 

 diameter almost ceases. As soon as the ' stone ' has become 

 firm the fruit begins again to increase in diameter, the chief 

 growth in thickness taking place in the mesocarp. 



3. A glucoside, known as amygdalin, is present in the bark, 

 leaves, and seeds of many species of this genus : it is a non- 

 poisonous compound, but under the influence of the enzyme, 

 emulsin, which is often associated with it, amygdalin decomposes 



