220 PEACTICAL BOTANY. 



blotting-paper, and ignite them in a spirit lamp on platinum foil, 

 or on a cover glass ; then treat the ash with weak acetic acid ; 

 mount the residue, and examine under a high power : a skeleton 

 will then be found to remain, which represents clearly the several 

 details of structure of the epidermis above described. From the 

 treatment which the preparation has undergone it may be 

 concluded that this is a skeleton of silica. 



VII. Cut radial longitudinal sections of an internode 

 of an underground stem : wash them well with water 

 to remove as much as possible of the starch, and mount 

 some of them in glycerine, others in Schulze's solution. 

 Note successively the following tissues 



1. The oblong superficial cells with brown walls, 

 frequently bearing unicellular hairs. 



2. The oblong cells of the Cortex with cellulose 

 walls, and containing starch. 



3. The Vascular bundles, which may be easily 

 recognised as transparent bands of tissue, in which 

 may be clearly seen 



a. The elongated Tracheides of the xylem, showing 

 annular, spiral, or irregularly reticulate thickening 

 of the walls : these thickenings stain yellow with 

 Schulze's solution : there are no protoplasmic contents : 

 the lignified rings are often found free in the inter- 

 cellular cavities, owing to the rupture of the thinner 

 parts of the walls : for this reason also the annular 

 vessels, which adjoin the intercellular cavities in the 

 bundles, are frequently not to be found in transverse 

 sections. 



1. The Phloem consisting of 



a. Sieve-tubes, which- are elongated elements, with 

 cellulose walls, and granular protoplasmic contents, 



