52 PRACTICAL BOTANY. 



Chlorophyll grains (cf. infra) may be found in them : this is 

 an exceptional case, as they are usually absent from cells of the 

 epidermis. 



The cells surrounding the bases of the hairs are 

 extended radially (as regards 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. 



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 Schulze's solution (cellulose) : 

 they are specially thickened at the angles, where three 

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

 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. 



Observe carefully the resin-passages, which occur 

 in the cortical parenchyma. (N.B. The resin, being 

 soluble in alcohol has been removed. To see it in its 

 original condition sections may be cut from the fresh 

 stem, and stained with tincture of alkanet.) They are 

 inter-cellular spaces, formed by the splitting of cell- 

 walls. The cavity thus formed is surrounded by small, 

 thin- walled, epithelium, the cells of which divide both 

 radially, and tangentially as regards the passage. 



