62 PRACTICAL BOTANY 



Examine the medullary rays in the xylem : they are com- 

 posed of oblong cells, with their longer axes horizontal, arranged 

 like bricks in a wall : in characters they resemble xylem- 

 parenchmya. 



8. The pith presents in radial section, for the most part, the 

 same characters as those already noted in transverse section. 



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

 small quantity of Schulze's macerating fluid (see Appendix A) 

 in a test tube, and warm gently till the tissues break up, and 

 the several constituents begin to separate : then wash with 

 water, and mount a very small quantity in water or glycerine. 



Some at least of the constituents will be found lying sepa- 

 rately, or may be detached by slight pressure on the cover- 

 slip : the true form of the wood-fibres, as greatly elongated, 

 spindle-shaped cells, will now be seen. Note also vessels of 

 the various types above described, and xylem-parenchyma. 



VII. Cut tangential sections through the xylem of a four to 

 five-year-old stem of Elm, treat with solution of iodine, and 

 mount. Observe first with a low power 



1. The medullary rays of lenticular outline, easily recognized 

 as masses of small thick- walled cells of almost circular form, 

 filled with starch, which appears dark blue. This is best seen 

 in stems cut in autumn. Examine the medullary rays closely 

 in the thinnest part of the section, under the highest power, 

 and note the small triangular intercellular spaces, which take 

 a horizontal course along the medullary rays, and are therefore 

 cut here transversely. In close connection with these 



2. The xylem-parenchyma, the cells of which also contain 

 starch, and are thus easily recognized : note that cells of the 

 parenchyma more or less completely surround 



3. The vessels, the walls of which are stained yellow, and 

 present those characters already observed in radial sections. 

 The interspaces are filled by 



4. Masses of xylem-fibres, which appear as before. 



VIII. Cut tangential sections of the phloem of a similar 

 stem : treat as before, and observe 



I. The form and arrangement of the medullary rays as in 

 the xylem, but the walls of the cells are thinner, and not 



