334 PRACTICAL BOTANY 



recognized 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 

 chlor-zinc-iodine : 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, 

 and are divided into joints by transverse or oblique 

 walls : they correspond in general characters to the 

 sieve-tubes of the higher plants, but the sieve-structure 

 of the terminal walls is not clear. Numerous highly 

 refractive granules are found on both sides of the 

 terminal walls. 



ft. Cambiform cells of oblong form, with cellulose 

 walls. 



VIII. From buds which have been hardened in alcohol 

 cut median longitudinal sections : treat them for a 

 short time with a strong solution of caustic potash, then 

 wash them with water, and mount in strong acetic acid : 

 or the sections may be treated with " eau de javelle " 

 and be mounted in glycerine. 



Examine them first with a low power, and observe 

 that the nodes and internodes are easily recognized 

 in the lower, older parts of the sections ; the former 



