LENTICELS 



479 



The perviousness of lenticels to gases might be inferred from their 

 anatomical structure. Beneath every lenticel the intercellular spaces 

 of the cortex are continued as passages right across the lenticellar 

 meristem into the complementary tissue, where they ramify in every 

 direction. Since the closing layers, if such are present, are also 

 perforated, and since the epidermis becomes ruptured over every fully 

 developed lenticel, an open communication is established between the 

 cortical ventilating system and the outer air. Experimental proof of the 

 pneumathode function of lenticels is also easily obtained in the fol- 

 lowing manner: One end of a severed twig, bearing lenticels, is occluded, 

 by coating it with wax or in some other way, while the other is 

 attached to the shorter arm of a J -tube; the whole apparatus is then 

 placed in water so that the twig is completely immersed. If mercury 

 is now poured into the longer arm of the J -tube, a rapid stream of air- 

 bubbles will escape from the lenticels even under a small excess 

 of pressure. 



What has been stated regarding the significance of lenticels for 

 gaseous interchange in general, naturally applies to the case of trans- 

 piration in particular. Lenticels are by no means as important as 

 stomata in this connection; nevertheless, the author has thought it 

 worth while to collect some numerical data concerning the value of 

 lenticels as paths of transpiration. The method employed was that of 

 direct weighing. Pieces of moderately old branches of various trees 

 were rendered airtight at both ends by means of sealing-wax. The 

 lenticels of some of these pieces were closed with asphalt varnish. 

 On other pieces, which served as controls, an equal number of 

 areas of periderm, of the same size as the lenticels, were similarly 

 coated with varnish. The loss of weight by transpiration was observed 

 daily for both sets of branches, and in this way a quantitative estimate 

 of the influence of the lenticels upon transpiratory activity was 

 obtained. A selection from the results of these experiments is repro- 

 duced in the accompanying table. The figures represent the loss of 

 weight in a stated period of time, expressed as a percentage of the 

 initial weight of the twig. 



