ELM STEM 105 



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, 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 hori- 

 zontal 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 com- 

 pletely 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 



1. The form and arrangement of the medullary 

 rays as in the xylem, but the walls of the cells are 

 thinner, and not lignified : intercellular spaces may be 



