LENTICELS 



477 



ig normally very much distorted; occasionally the pore passage is also 

 retained, but the back-cavity and internal air-chamber have always dis- 

 appeared completely. This transformation of some of the guard-cells, 



m 



Fig. 189. 



Modified stomata from the inner surface of the pitcher of Nepenthes Rofflesiana, in 

 their natural positions. A. Both guard-cells still clearly recognisable. B. Lower 

 guard-cell greatly reduced, but still furnished with its external cuticular ridge. 

 C. Lower guard-cell entirely reduced. D. Front view of a completely modified 

 stoma. After Bobisut. 



in Nepenthes, into structures which assist in the capture of insects, 

 is one of the most remarkable instances of secondary adaptation that is 

 to be met with in the whole field of physiological anatomy. 



9. Lenticels? u 



The periderm, like the epidermis, is perforated at a number of 

 points by pneumathodes, which in this case are termed lenticels (the 

 name is due to De Candolle). The mode of development of these 

 structures clearly indicates their physiological affinity with stomata ; 

 for, on the young shoots of our native trees and shrubs, every lenticel 

 arises as Unger discovered long ago immediately beneath a stoma, the 

 functions of which it assumes, when the epidermis is replaced by periderm. 



A fully developed lenticel is a biconvex (lenticular) mass of special 

 tissue, embedded in the periderm. Its inner boundary is marked by a 



