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latin, the oxygen issuing from the stomata directly comes into contact with the 

 gelatin, and a luminous spot appears shaped like the leaf. 



In performing this experiment it is advisable to cut one and the same leave into 

 two halves and press at once both parts on the gelatin, one with the upper- the other 

 with the underside. 



The process can, however, become very complicated by the closing of the sto- 

 mata, which are extremely sensitive to the contact of the salt-containing culture-gela- 

 tin, and evidently also to the absence of oxygen in their surrounding, when kept in 

 the dark. 



The fact that nyctitropic leaves evaporate the most vigorously at that side, 

 which is covered during the night, has been confirmed by the photobacteria-method 

 respecting the secretion of oxygen. So, the clover-leaf closes at night by putting the 

 upper surfaces of the leaflets against one another: hence these surfaces must exhibit 

 a. more energetic secretion of water-vapour, and in the light, of oxygen, then the 

 under surfaces, which has been confirmed by the experiment. 



For Robinia pseud-acacia, where at night the under surfaces cover each other, 

 the most vigorous secretion of oxygen is to be expected in the light from the under- 

 side, which is likewise confirmed by the experiment. But with Robinia the difference 

 is less considerable than with clover. 



