70 PKACTICAL BOTANY. 



Examine the several tissues, above enumerated, in 

 detail with a high power : 



1. Epidermis : a single layer of cells, with the outer 

 wall thickened and cuticularised (test with the usual 

 reagents) : Stomata will be found in a normal posi- 

 tion in young twigs, in older ones they are found at the 

 apices of the lenticels (cf. infra, p. 72). Note the form of 

 the conical hairs, the walls of which are silicified. 



To obtain proof of the latter fact, treat tangential sections of 

 the surface of the stem with potassium chlorate and nitric acid ; 

 dry them with blotting paper and ignite on a cover slip, or plati- 

 num foil ; mount the ash in water, and treat with nitric acid. 

 Silicified walls will after this treatment present the same out- 

 line as they originally did. In this case complete skeletons of the 

 conical hairs will be found. 



2. The Cork (when present) lies immediately below 

 the epidermis : it consists of cubical cells, with thin 

 walls, and little or no cell-contents : they are arranged, 

 in radial rows, without intercellular spaces. Select 

 a thin part of the section for special study of these 

 radial rows, and note in each the following succession 

 of tissues, passing from without inwards : 



a. A series of Cork cells as above described : walls 

 stained yellowish-brown with Schulze's solution (Peri- 

 derm). 



6. At least one cell with very small radial diameter, 

 and with protoplasmic contents and thin cellulose walls 

 Cork-cambium or Phellogen. 



c. Cells with thick cellulose walls, and protoplasmic 

 contents with chlorophyll : no intercellular spaces : 

 this is the Phelloderm, which is also derived from the 

 cork-cambium. 



