88 LEAVES. 



(48) Tea. 



The leaves of Camellia Thea, Link. (N.O. Ternstrcemiacece), 



The upper epidermis is composed of cells with undulating walls 

 and covered with a rather thick cuticle. The lower epidermis 

 consists of smaller cells and is alone provided with stomata ; the 

 latter are surrounded by three or four tangentially elongated cells. 



Simple hairs occur on both surfaces of the leaf, but they are 

 more abundant on the lower; the number, however, varies with 

 the variety of tea, and with the age of the leaf ; they are unicellular, 

 tapering and rather thick walled, varying very much in length, but 

 often attaining 500-700/x. 



The mesophyll is heterogeneous and asymmetrical. It is 

 characterised by the presence of a large number of sclerenchymatous 

 idioblasts. These are more or less branched and warty and often 

 extend transversely from the upper to the lower epidermis. They 

 vary very much in shape and in the thickness of the walls. The 

 cells of the spongy parenchyma contain cluster crystals of calcium 

 oxalate. 



The midrib is biconvex. Under each epidermis there is a layer 

 of collenchyma of varying thickness. The wood is arched and the 

 bast contains crystals of calcium oxalate. The meristele is sur- 

 rounded by a pericycle consisting of slightly lignified cells arranged 

 in circle. The cortical tissue contains idioblasts which are usually 

 rather larger and more branched than those of the mesophyll. 



The little fragments of the stems, which are often to be found in 

 ordinary tea, have a slightly different structure. The wood in them 

 forms a circle within which there is a pith containing branched 

 idioblasts ; these have comparatively thin, pitted walls. 



The diagnostic characters of powdered tea are : 



(a) The characteristic hairs. 



(b) The sclerenchymatous idioblasts, especially in petiole and 

 midrib. 



(c) The stomata surrounded by tangentially elongated cells. 



(d) The calcium oxalate in cluster crystals. 



