CH. IV] LENTICELS. 99 



(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 

 india-rubber tube. The vessels and intercellular spaces at 

 the upper (free) end of the stick are to be secured by an 

 india-rubber tube wired on and closed by being folded 

 down parallel to the branch and again wired. The 

 U tube is placed in a jar of water so that the stick is 

 immersed, and mercury is poured into the long arm: 

 after a varying time air is seen to issue in fine streams 

 from the lenticels, — that is if they are open. Fifteen or 

 20 cm. of mercury is sufficient pressure. 



(126) Bloom. 



The character of the leaf-surface has an eflfect on 

 ■transpiration, as may be shown in the following way'. 

 Bring into the laboratory a pot of Kleinia or Cotyledon, 



1 See Garreau, Ann. Sc. Nat. S. 3, T. xiii., p. 339. 



7—2 



