110 LENTICELS. [CH. IV 



(123) Opening and dosing of stomata'^. 



The majority of stomata close when surface-sections 

 of the leaf are placed in water. Some leaves however 

 behave in the reverse way: of these the most easily 

 accessible are those which form the floating rosettes of 

 Callitriche. If the tissue of the lower surface of the leaf 

 is gently scraped away with a needle, and the leaf is 

 mounted in water with the upper surface upmost the 

 stomata are visible ; they can be made to close by 

 irrigation with 2*5 p.c. NaCl solution, and again to open 

 by replacing the salt solution with water. 



(124) Electric effect'-. 



Strips from the under-surface of the leaf of Ranunculus 

 ficaria are mounted dry under a cover-glass, on a slide 

 bearing a pair of microscopic electrodes. On passing the 

 induced current the stomata close. A current, slightly 

 stronger than that bearable on the tongue, is necessary. 

 If Callitriche is used it must be mounted in water: a 

 stronger current is needed. 



(125) Lenticels\ 



The fact that lenticels communicate with intercellular 

 spaces may be conveniently studied in connection with the 

 parallel results obtained with stomata. Fit a woody 

 dicotyledonous branch (dog-wood, Cornus sanguinea, does 

 well) to the short arm of a U tube by means of firmly wired 



1 Mohl, Botaii. Zeitimg, 1856 ; N. J. C. Miiller, Pringsheim's Jahrh. 

 VIII. p. 75 ; Leitgeb, MUtheilungen Bot. Institut Graz, 1886. 



- N. J. C. Miiller, P ring she iiii's Jahrh. viii, 



■^ Stahl, Botan. Zeitung, 1873, p. 613 ; the author recommends Gingko 

 hiloba, Samhucus nigra and Lonicera tatarica. 



