150 PEACTICAL BOTANY. 



C. A broad band of chlorophyll-containing Meso- 

 phyll, with resin-passages. 



D. A Bundle-sheath, consisting of oval cells. 



E. A broad band of tissue without chlorophyll, which 

 surrounds 



F. Two central Vascular bundles. 



Study these several tissues under a high power. 



A. The Epidermal cells have their thick walls 

 differentiated into three layers. These may be 

 recognised without staining, or better after treatment 

 with Schulze's solution, as 



i. A thin external Cuticle, not very deeply stained. 

 It extends as wedge-like processes between the cells. 



ii. The Cuticularised layers, forming a thick band, 

 which stains a deep brown. Immediately surrounding 

 the cell- cavity is 



iii. A broad pitted band, not deeply stained. 



This differentiation may be brought into greater prominence by 

 treating (a) with strong sulphuric acid, or (6) by staining 

 slightly with fuchsine. (c) If sections are boiled for ten 

 minutes or more in strong solution of potash, i. will be dissolved 

 while ii. and iii. remain. 



Note the larger cells at the angles of the section, 

 with thicker walls. 



Here and there depressions of the external surface 

 may be observed. These indicate the position of the 

 Stomata. Observe the two guard cells, which are 

 seated some distance below the surface of the leaf. 



B. The Hypoderma (sclerenchymatous) varies in 

 thickness from a single layer of cells to several layers. 

 It is thickest at the corners of the section ; cells thick- 



