ELM. STEM. 79 



Examine the medullary rays in the xylem : they 

 are composed of oblong cells, with their longer axes 

 horizontal, arranged like bricks in a wall : in characters 

 they resemble xylem parenchyma. 



8. The Pith presents in radial section, for the most 

 part, the same characters as already noted in transverse 

 section. 



VI. Treat some small pieces of the wood of the Elm 

 with Schulze's macerating fluid (potassium chlorate, 

 and nitric acid), and warm gently till the tissues break 

 up, and the several constituents begin to separate : then 

 wash with water, and mount in water or glycerine. 



Some at least of the constituents will be found lying 

 separately, or may be detached by slight pressure on 

 the cover slip : the true form of the wood-fibres will 

 now be seen. Note also vessels, and xylem-paren- 

 chyma. 



VII. Cut tangential sections through the xylem of 

 a 4-5 years' old stem of Elm, treat with solution of 

 iodine, and mount. 



Observe first with a low power 



1. The Medullary rays of lenticular appearance, 

 easily recognised as masses of small thick-walled cells, 

 filled with starch, which appears dark blue. (This 

 is best seen in stems cut in autumn.) In close connec- 

 tion with these 



2. The Xylem-parenchyma, the cells of which 

 also contain starch, and are thus easily recognised : 

 note that it more or less completely surrounds 



3. The Vessels, the walls of which are stained 

 yellow, and present those characters already observed 

 in radial sections. The interspaces are filled by 



