72 PKACTICAL BOTANY. 



stoma at the apex of the lenticel : the whole mass of 

 tissue consists of cells of a corky nature, with inter- 

 cellular spaces. 



By comparison of sections of twigs of various ages it may be 

 seen that lenticels originate below the stomata, by divisions of 

 the subjacent cortical tissue by walls both radial and tangential ; 

 secondary lenticels are also formed later ; these appear at points 

 independent of the stomata. 



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 constant. 



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 is tangentially ex- 

 tended, so as to keep pace with the increasing bulk of 

 the internal tissues. 



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



4. The Sclerenchyma consists of cells with walls 

 so; thickened that the cell-cavity is often obliterated ; 

 the walls are differentiated into two or more strata. 

 Reactions with aniline sulphate, light yellow ; with 

 Schulze's solution; brownish red. 



5. The Soft bast is, as in the Sunflower, composed 

 of several different thin-walled tissue-elements, which 



