ELM STEM ' 100 



c. Fibres (sclerenchyma), by elon- 

 gation and interweaving of 

 cells, the width of the cells 

 at the same time being re- 

 latively reduced : the ends of 

 the cells slide past one another 

 as the cells elongate. 



(ii.) Xylem. a. Vessels, by lateral distension, 

 and absorption of cell- contents, 

 and of the oblique walls. 



b. Parenchyma, by division of the 



cells by transverse septa. 



c. Fibres, by elongation and inter- 



weaving of the cells, while the 

 width of the individual cells 

 is relatively reduced. 



Observe intermediate stages between cambium-cells 

 and these several mature tissues : this may best be 

 done in sections cut from stems in early summer. 



X. To investigate the nature of the crystals, 

 several times observed in the parenchyma of the stem 

 of the Elm, cut tangential sections of the phloem or 

 of the cortical tissue, mount in water, and having 

 found one or more crystals 



(i.) Run some iodine solution under the cover-slip : 

 the crystal is not stained. 



(ii.) Acetic acid : it is not attacked. 



(iii.) Dilute nitric acid : it is more or less completely 

 dissolved. 



These reactions, coupled with what is known from 

 the analysis of ash, point to the conclusion that these 

 are crystals of calcium oxalate. 



