492 



The Journal of Heredity 



These facts have led many plant 

 ])hysioloj:?ists to think that. althou<:;;h 

 the Icnticcls undoubtedly do fulfil in 

 many cases the function of breathing 

 pores for the bark, that is not really 

 their purpose. Such a solution of the 

 problem accords well with the interpreta- 

 tion of nature of certain scientists, who 

 hold on ijhilosophical grounds that 

 nothing should be said really to have 

 a purpose. 



EXPERIMENTAL TESTS 



But whether breathing is the purpose 

 of the lenticel or not, one can very 

 easily demonstrate that it actually does 

 act in most ca.ses as an outlet for the 

 plant's ventilating system. A favorite 

 laboratory experiment is to seal up one 

 end of a stick, seal a tube around the 

 other end, and then force air under 

 pressure through the stick, submerged 

 in water. A string of fine bubbles 

 will issue from every lenticel. The 

 fact can be demonstrated even more 

 easily, merely by sealing both ends of a 

 short stick and then submerging it in 

 warm water; the warmth will in most 

 cases be sufficient to expel the cooler air 

 within the stick, and bubbles will appear 

 at the lenticels. 



Sometimes these openings reach a 

 length as great as a third of an inch; 

 in other cases, as in the bark of the 

 sycamore (Platanus), thc\' are so small 

 as to be almost microscoj^ic. In twigs 

 they are commonest on the under side, 

 and the number increases somewhat 

 regularly with the age of the wood. 

 On a piece of elm branch 20 centimeters 

 long, Haberlandt found the numlxT of 

 lenticels as follows: 



Upper side. . 

 Under side. . 



First 

 year 



.S.S 

 . 70 



Third to 

 fifth 

 y>ar.s 



66 



7« 



Tenth to 



fifteenth 



years 



9.S 

 •>6 



ON A MOIST DAY 



Twig of a Chinese magnolia, highly 

 magnified. The dry, powdery cells 

 which fill the breathing jjores of 

 the l)ark have absorl)e(l moisture 

 from the air, imtil they have swelled 

 out and ])rotrude like warts. One 

 of the ftmctions of the lenticels is to 

 regulate the transpiration of mois- 

 ture between the interior (>{ the tree 

 and the outside air. (Fig. 4.) 



The lenticels usually begin formation 

 under the surface, frequently bene:ith 

 one of the stomata, in which case, as 

 the ei)idermis is gradually rei)laced by 

 cork (?'. t'., bark), the lenticels lake the 

 place of the stomata as ventilating jjores. 



Structurally, the lenticel may be 

 descril)efl in simplest terms as an ojjen- 

 ing throtigh the bark, which is filled, 



