400 AURANTIACE^E, OB ORANGE TRIBE. 



which form a leaf ; and that in some carpels, the resemblance to 

 a leaf is very distinct (. 462). Supposing the two edges of the 

 carpellary leaf to be folded together, as represented in Fig. 97, 

 we should have the cuticle of the under surface becoming the 

 lining of the cavity, the cuticle of the upper surface forming its 

 external wall, and the parenchyma or fleshy tissue of the leaf 

 intervening between them. The amount of this parenchyma is 

 subject to much variation ; and the two cuticles often undergo 

 great changes in structure and degree of density. The ovarium 

 of the Orange is to be regarded (as already stated) as made up 

 of a considerable number of carpels adherent to each other ; and 

 in its early condition, the walls of these are everywhere of the 

 same firm fleshy character. During the ripening of the fruit, 

 however, the rind or external wall is separated from the inner 

 wall by a quantity of spongy parenchyma, which in some species 

 (as the Shaddock) attains a very considerable thickness ; the 

 outer walls of all the carpels unite together to form one conti- 

 nuous envelope ; whilst the inner walls, enclosing the pulp and 

 seeds, are easily separated from this and from each other. In 

 the Plum, Cherry, Peach, and other stone fruits, which belong 

 to the order Rosaceas, the change is still more decided. In these, 

 each fruit, which is the ripened ovary, contains but one cell ; 

 and each cell usually includes but a single ovule when mature, 

 though at an earlier period it may have contained several. Now 

 th* lining or inner wall of the ovary here becomes greatly con- 

 densed, forming the stone; the outer membrane continues to exist 

 as the cuticle or skin of the fruit ; and it is the fleshy part of the 

 carpellary leaf, very much increased in amount, that forms the 

 edible portion. In such instances, the outer is called the epi- 

 carp, the inner wall or stone the endocarp, and the succulent flesh 

 the sarcocarp. 



566. The various species of the Orange tribe are almost all 

 natives of the East Indies and China, whence they have been 

 transported to other countries within or near the tropics. They 

 nearly all contain sugar, citric acid, an aromatic essential oil, 

 and a bitter principle having tonic properties; but these are 

 combined in varying proportions in different fruit. Thus in the 



