98 MOVEMENTS OF STOMATA. [CH. IV 



the tube is held in the mouth, and the leaf is immersed 

 in water: by blowing gently, bubbles are forced out of 

 the stomata on the external surface. Now clean the 

 bloom from a zone of the leaf, which may be done by 

 gently rubbing it with a plug of cotton wool dipped in 

 warm water. 



On again immersing the leaf and blowing, it will be 

 seen that the air does not come out of the cleaned zone, 

 which is now thoroughly wetted owing to the removal of 

 the bloom. 



When onions are not available, the flower stalk of 

 Narcissus answers well. A rubber tube can be slipped 

 over the cut end, and the stalk plunged upside down 

 flower and all, into a jar of water. The stalk should not 

 be cut too near the ground but where it begins to be 

 hollow. 



(123) Opening and closing 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 irriga- 

 tion with 2-5 NaCl solution and again to open by replacing 

 the salt solution with water. 



The stomata of Trianea hogotensis are also useful for 

 similar experiments. 



