90 LEAVES. 



(49) Tobacco Leaves. 



The leaves of Nicotiana Tabacum, Linn. (N.O. Solanacese). 



The epidermis of both surfaces is furnished with simple and 

 glandular hairs and also with stomata. The cells of the upper 

 epidermis are polygonal and have slightly wavy walls, whilst 

 those of the lower epidermis are sinu us. 



The stomata are surrounded by three cells, one of which is 

 smaller than the others. 



The simple hairs are uniserial and conical. The glandular 

 hairs vary in appearance. Some are long, uniserial and ter- 

 minated by a unicellular, bicellular, or pluricellular gland ; 

 others are shorter and consist of a very large pluricellular gland 

 borne upon a one-celled pedicel. 



The mesophyll is heterogeneous and asymmetrical ; the cells 

 of the spongy parenchyma are oval or polygonal, and some of 

 them are filled with sandy crystals of calcium oxalate. The 

 wood of the midrib is arched and the bundles bicollateral. 



The diagnostic characters of powdered tobacco leaves are : 



(a) The characteristic hairs. 



(b) The cells with crystal sand. 



(c) The absence of pericyclic fibres. 



