144 PRACTICAL BOTANY 



ii. The cuticularized layers, forming a thick band, which 

 stains a deep brown. Immediately surrounding the cell-cavity 

 is 



iii. A broad pitted band, not deeply stained. 



Here and there depressions of the external surface may be 

 observed. These indicate the position of the stomata. Ob- 

 serve 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, chlorophyll-con- 

 taining 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 scler- 

 enchyma. 



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 



i. Parenchymatous cells, with thin cellulose walls (blue 



with chlor-zinc-iodine), and protoplasmic contents, 

 ii. Elements having lignified walls, with bordered pits, 

 and no cell-contents (tracheides, or "transfusion- 

 tissue"). 



6 The two central vascular bundles, the constituents of which 

 resemble those of the stem. Note that the xylem is directed 

 towards the upper surface. Thick-walled sclerenchyma is 

 scattered irregularly round the bundles. 



A description of the root is given in the larger edition. 



