234 PRACTICAL BOTANY 



protoplasmic contents with chlorophyll. Many cells 

 have recently divided : this is necessary to keep pace 

 with the growth in thickness of the vascular cylinder. 

 Large intercellular spaces (resin-passages) occur here 

 and there, and are lined with small-celled epithelium. 

 (Compare p. 65). 



It must be remembered that in the present case the resin itself 

 has been dissolved out by. alcohol : sections should, therefore, be 

 made from fresh material in order to see the secretion in situ. It 

 appears amorphous and transparent : it is soluble in alcohol, 

 leaving a slight residue. 



The secretion stains deeply with tincture of alkanet. (See 

 p. 65.) 



Near the periphery of the cortex will be found a layer 

 of cork and a cork-cambium (compare stem of Elm, 

 p. 91), derived from cells of the cortex by their division 

 by tangential walls. The cells of the cork have no cell- 

 contents : their walls are coloured yellowish brown with 

 chlor-zinc-iodine. 



Treat a section with strong sulphuric acid. The walls of the 

 cork retain their sharp contour. 



At the bases of the indentations at the margin of the 

 section, and immediately below the epidermis, note 

 groups of sclerenchyma, having thick lignified walls 

 (yellow with chlor-zinc-iodine). 



3. The vascular system is here a complete ring, 

 though it is composed of separate bundles in the bud 

 (see above, p. 232) : distinguish as before, the external 

 phloem, the internal xylem, and the misty layer of 

 cambium. 



The vascular bundles were seen to be separated in 



