106 STOMATA. [CH. IV 



of glass and leaf. Iv}'- leaves treated in this way give 

 striking results in winter, the paper on the upper side 

 remaining blue for as long as 24 hours. 



(118 b) Closure of stoinata in half-iuithered leaves. 



For this experiment Stahl^ recommends Tropwolum 

 wiajus and Ghelidonium majus, and we have found Impa- 

 tiens noli-me-tange7'e useful. One out of a pair of similar 

 leaves of Impatiens is gathered and allowed to lie on the 

 table ; as soon as it shows obvious flaccidity the fresh leaf 

 is gathered and the two are placed lower side upmost on 

 a soft dry folded cloth, covered with dry cobalt paper and 

 then with a glass plate about 10 cm. x 10 cm. The cloth 

 yields slightly and allows close contact between the 

 surfaces of cloth, leaf, paper and glass without danger of 

 injuring the leaf The paper over the withered leaf 

 remains blue after the fresh leaf has reddened the other 

 piece of paper. 



(118 c) Closure of stomata by treatment ivitli salt solution. 

 StahP has shown that young plants of Acer pseiido- 

 platanus, seedlings of Tropceolum majus, Phaseolus midti- 

 florus and Zea niais grown in pots and watered with 

 -J- p.c. NaCl solution exhibit closure of stomata after a few 

 days' culture. Leaves taken from the experimental plants 

 are subject to the cobalt test with similar leaves from 

 plants which have not been watered with salt solution. 

 He describes the stomatal surface of the experimental 

 leaves as not reddening the paper for a long time, whereas 

 the control leaves behaved normally. 



1 loc. cit. p. 120. - loc. cit. p. 134. 



