156 FRUITS. 



(79) Colooynth Fruit. 



The fruit of Citrullus Colocynthis, Schrader (N.O. Gucurbitaceae). 

 The pericarp presents the following structure : 



(1) An outer epidermis composed of polygonal cells with 

 strongly suberised outer walls. 



(2) Several rows of parenchymatous cells ; these are sometimes 

 collapsed, sometimes tangentially elongated, and thickened at 

 the angles to form a collenchymatous layer. 



(3) A layer of several rows of sclerenchymatous cells with 

 thickened pitted walls ; the inner cells of this layer are radially 

 elongated. 



(4) A parenchymatous tissue composed of large polygonal, 

 rounded, or oval cells, on some of which pitted areas are very 

 distinct. This parenchymatous tissue, of which the pulp of the 

 fruit is composed, is traversed by numerous bicollateral fibro- 

 vascular bundles, some of which are accompanied by tubular 

 idioblasts containing the active principle. 



The seed exhibits the following layers : 



(1) An outer hyaline layer consisting of a single layer of flat- 

 tened cells which swell in contact with water. 



(2) A layer of palisade cells, the walls of which exhibit 

 bar-like thickenings ; these cells often contain a brown granular 

 substance (in ripe seeds). 



(3) A highly developed sclerenchymatous layer, the cells of 

 which vary greatly in size and shape. Some have moderately 

 thick pitted walls, but in most of them the walls are so thick 

 as almost to obliterate the lumen, and are traversed by branch- 

 ing pits. 



(4) A layer composed of a single row of coarsely pitted or 

 reticulate cells which exhibit dome-like projections towards the 

 interior of the seed; this layer is very characteristic. 



(5) A layer of two or more rows of parenchymatous cells 

 which in surface view are elongated ; the cells of one of these rows 

 are spirally thickened, giving the tissue a very characteristic 

 appearance. 



(6) The cotyledons are composed of thin-walled cells containing 

 fixed oil and small aleurone grains in which a globoid is easily 

 visible ; the epidermal cells of the cotyledons have smooth, 

 straight walls. 



The diagnostic characters of the powdered pericarp are : 



(a) The epidermal cells, especially in section. 



(b) The fderenchyma of the rind with mod rately thick 

 ivalls. 



(c) The large empty parenchymatous cells, often with 

 distinct pitted areas. 



Of the powdered seed : 



(d) The very characteristic palisade cells. 



(e) The sclerenchymatous ring. 

 (/) The reticulate cells. 



(g) The spirally striated cells. 



