ABSORPTION TISSUES 119 



Lenticels. — Lenticels are respiratory openings in 

 the periderm or corky covering tissues of mature 

 woody plants. These openings expose the tissues 

 immediately beneath the cork and air thus gains access 

 to these cells. On surface view the lenticel appears 

 as an elliptical or oval scar raised above the surround- 

 ing tissues. Microscopic examination of sections 

 through a lenticel shows a break or gap in the cork 

 cells through which the inner bark tissues are exposed 

 (Plate 44). The inner bark cells in the vicinity of 

 a lenticel are loosely connected and large intercellular 

 spaces are apparent. Lenticels are not mere chance 

 fissures in the bark, but are formed from the meriste- 

 matic tissue (phellogen) which produces cork. At 

 points of formation the phellogen produces a group 

 of compact cells, which are gradually forced outward 

 until they rupture the existing cork layer, thus giving 

 rise to a lenticel. 



