STRUCTURE OF THE ORANGE. 427 



cleft-like pits. The tangentially-elongated inner elements of the 

 spermoderm are arranged at right angles to the preceding. 



Structure of the Orange. The cross- section through a ripe 

 orange, Citrus vulgaris (C. aurantium), shows externally the 

 part designated rind, and internally the " segments " tilled with 

 the orange-red flesh, the number of which segments is uncertain, 

 and varies from six to twelve. The segments are separated by 

 thin membranes, which combine into a central column of tissue. 

 If we wish to apply the customary designations of the parts of a 

 fruit to the structure of this, we can speak of the outer rind as 

 epicarp, the orange-red flesh as mesocarp, the inner column of 

 tissue and the partition walls as endocarp. 



We pass now to a microscopical study of the individual parts. 

 In delicate cross-sections through the rind we see most externally 

 a small-celled epidermis, to which succeeds a tissue of gradually 

 enlarging cells. The epidermis and adjoining tissue contain 

 orange-red chroma tophores, which farther inwards disappear. 

 Intercellular spaces filled with air appear here between the cells, 

 and gradually enlarge, since the tissue itself* acquires the char- 

 acter of a looser spongy parenchyma. The rind is traversed by 

 vascular bundles, which the cross-section lays bare chiefly in their 

 longitudinal course, and which branch towards the periphery. 

 Adjoining the epidermis are the large glands of ethereal oil, 

 visible to the naked eye. They show throughout the structure 

 known to us from Euta, and allow the inner investment of delicate 

 cells to be readily distinguished. The fruit, observed macroscopi- 

 cally from the outside, shows the oil-glands as darker spots, the 

 tissue separating them as a brighter network. 



A delicate surf ace- sect ion of the outer side shows us first the 

 small polygonal epidermal cells. Those lying over the oil-glands 

 are distinguished by absence of the orange-red chromatophores ; 

 they contain in place of them colourless globules of various sizes. 

 Scattered in the epidermis are the stomata, devoid of protoplasm, 

 and closed inwards. The next deeper sections give instructive 

 views of the oil-glands, and terminations between them of the 

 vascular bundles. Still deeper sections show the spongy tissue, of 

 elongated sac-like cells. Adjoining the loculi of the ovary the 

 cells of the rind become still longer, fibrous, in part strongly 

 thickened and then provided with narrow, obliquely mounting 

 pits. The partitions between the " segments " are constructed in 

 the same way : in the interior, of spongy parenchyma ; outwardly 



