62 PRACTICAL BOTANY 



Mount some of these in glycerine or glycerine jelly 

 (these may be kept as permanent specimens), and 

 others in chlor-zinc-iodine. Examine these first with 

 a low power, and observe the following tissues in 

 succession, starting from the exterior : 



1. The epidermis, a single peripheral layer of cells, 

 not very well defined from the underlying tissues : it 

 completely covers the surface. 



The margin is not perfectly regular, but is here and 

 there extended outwards at the regions surrounding the 

 bases of the large multicellular hairs, which may be 

 recognized as being products of the epidermis. 



Since these hairs are usually injured in cutting the sections, the 

 width of their bases being greater than the thickness of a fine 

 section, in order to see them well thick sections should be made 

 specially, care being taken that the hairs shall not be previously 

 injured before the sections are cut. They will then be seen to be 

 long conical hairs with pointed ends, and divided by trans- 

 verse septa : their bases are embedded in cells of the epidermis 

 and underlying tissue, which together form at that point a small 

 emergence, on the apex of which the hair is borne. Other 

 smaller hairs also occur. Compare the description of the apical 

 bud (p. 82). 



2. Beneath this single epidermal layer lies a band of 

 tissue, several layers of cells in width, the walls of 

 which are thickened at the angles where three or more 

 cells meet, the cell-cavity being thus made oval or cir- 

 cular in transverse section ; this is the chief characteristic 

 of collenchyma, of which this is a good type. Below 

 this lies 



3. A band of thin-walled parenchyma, in which 

 are dotted here and there resin-passages. 



