64 PRACTICAL BOTANY 



may thus be easily recognized (see p. 39, reactions of 

 corky walls). 



The granular protoplasmic contents of these cells 

 (brown, with chlor-zinc-iodine : compare p. 27) are not 

 plentiful, but form a thin layer lining the somewhat 

 rounded cell-cavity. 



Chlorophyll-grains are to be found in these cells : this point 

 is to be noted, since in the stems of many plants chlorophyll is 

 absent from the epidermal cells. 



The cells surrounding the bases of the hairs are 

 extended in the direction of the radii of the stem and 

 the whole epidermis is at these points pushed outwards 

 owing to luxuriant growth of the underlying tissue : in 

 fact the hairs are each seated at the apex of an 

 emergence.. The nature of the hairs themselves 

 will be studied later in connection with the apical bud 

 (see p. 82). 



2. In the collenchyma the protoplasmic body 

 resembles that of the epidermis : chlorophyll-grains 

 are numerous. The cell-walls also are highly refrac- 

 tive, and stain blue with chlor-zinc-iodine (cellulose) : 

 they are specially thickened at the angles, where three 

 or more cells meet ; in the thickened mass the lines or 

 stratification are well seen. There is no sharp 

 internal limit to the collenchyma, but it merges 

 gradually into 



3. The thin-walled cortical parenchyma, which 

 differs from the preceding (a) in the thinness of its 

 walls, (&) its less copious cell-contents, (c) the larger 

 size of the cell-cavity, (d) the presence of intercellular 

 spaces, which result from the splitting of the cell- 



