LENTICELS. 151 



423. Lenticels are peculiar breaks in the continuity of the 

 periderm of dicotyledons. In some cases they can be detected 

 under minute elevations of the epidermis of the first year, which 

 split open either at the end of that season or during the next, 

 forming a rift running lengthwise of the stem. Through this cleft 



underlying tissues appear, protruding in an irregular manner, 

 the whole structure constituting a lenticel. According to Stahl, 1 

 there are two types of lenticels : 1 . Those with loose cells in the 

 rift, alternating with denser lines of cells. This is the most 

 common type, good examples being afforded by Alnus, Prunus, 

 ^Esculus, etc. 2. Those with closely united cells and with no 

 alternating denser lines. Illustrations can be found in Sam- 

 bucus (see Fig. 118), Salix, Cornus, etc. The same authority 

 states that in winter both of these kinds form an impervious 

 periderm-like layer. It appears from Stahl's examination that 

 in their complete and open state they aid in the exchange of 



gases between the interior and exterior of the stem. Klebahn 2 

 its base are in a healthy condition, while the internal shaft of wood is dry, and 

 not liable to undergo rapid decay. The formation of a separative mass over 

 the wood can therefore go on to completion. 



1 Bot. Zeit., 1873. Compare Haberlandt : Sitz. d. k. Akad. Wien, Band 

 Ixxii. Abth. i., 1875. 



a Berichte der deutschen botanischen Gesellschaft, 1883, p. 119. 



PIG. 118. Section through a lenticel in the periderm of Sambucus nigra: k, peri- 

 derm ; r, primary cortex ; v, ineristem, above which are the cells therefrom produced ; 

 6, liber. (Stahl.) 



