ELM STEM 93 



Examine points where a lenticel has been cut 

 through, or make median sections through a lenticel. 



Note that here the cork layer widens out laterally so 

 as to form a hemispherical mass (semicircular in section), 

 which is covered by the extended epidermis; if the 

 section be median, a stoma will usually be seen at the 

 apex of the lenticel : the whole mass of tissue consists 

 of cells of a corky nature, with intercellular spaces. 



By comparing sections of twigs of various ages it may be seen 

 that lenticels originate below the stomata, the subjacent cortical 

 tissue dividing by walls both radial and tangential ; secondary len- 

 ticels are also formed later ; these appear at points independent 

 of the stomata. 



The lenticels of the Elder (Sambucus') are of large size, and are 

 well suited for the study of their typical structure. 



3. The cortical tissue is a broad band consisting 

 of parenchymatous cells, with intercellular spaces. 

 According to their various characters they may be 

 thus grouped : 



a. Ordinary parenchyma cells, with cellulose walls 

 and protoplasmic contents with nucleus, chlorophyll, 

 and starch-granules : the two latter are not constantly 

 present. 



b. Cells (idioblasts) with large crystals, 



c. Large cells whose mucilaginous walls almost or 

 entirely obliterate the cell-cavity. 



Note that the cells (a) are subject to radial division, 

 and that the whole cortical tissue undergoes tangential 

 extension, so as to keep pace with the increasing bulk 

 of the internal tissues. 



N.B. No obvious bundle-sheath is present in this stem. 



