246 PRACTICAL BOTANY 



which stains a deep brown. Immediately surrounding 

 the cell -cavity is 



iii. A broad pitted band, not deeply stained. Com- 

 pare the epidermis of the Holly, p. 132. 



This differentiation may be brought into greater prominence by 

 treating with strong sulphuric acid, or by staining slightly with 

 fuchsin. 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 : an 

 intercellular space (respiratory cavity) is to be seen 

 immediately below each stoma. 



2. The hypoderma (sclerenchymatous) varies in 

 thickness from a single layer of cells to several layers. 

 It is thickest at the corners of the section : the cells are 

 thick-walled, and lignified. Note that it is absent 

 below the stomata. 



3. The mesophyll consists of thin-walled, chloro- 

 phyll-containing parenchyma : the cellulose walls (blue 

 with chlor-zinc-iodine) show a peculiar in-folding. 

 Resin-passages occur in it : their cavity is lined 

 with thin-walled epithelium, which is immediately 

 surrounded by a layer of thick-walled sclerenchyma. 



4. The endodermis has its walls stained brown with 

 chlor-zinc-iodine. 



5. The tissue immediately within this, which may be 

 called the pericycle, consists of two elements 



