22 



SCIENCE PROGRESS. 



ON THE PATHS OF EXIT OF CARBONIC ACID FROM 



LEAVES. 



Aided by this apparatus the author has been able to 

 carry out direct experiments on the two surfaces of living 

 leaves, and to determine what relation there is between the 

 distribution of the stomata and the amounts of CO, exhaled 

 in the dark or absorbed in bright light. In order to differ- 

 entiate between the two surfaces, the chambers figured below 

 have been designed. Two different pairs are represented. 



Each consists of a brass rim permanently closed on the 

 one side by a glass plate, and attached hermetically on the 

 other side to the surface of the leaf by a little wax, which 

 manipulation can easily be accomplished with the aid of a 

 hot wire. The rim is pierced by two fine metal tubes which 

 also pass through hemi-cylindrical blocks of brass by which 

 the chambers can be clamped together in their right posi- 

 tions on the two surfaces of a leaf. 



Two continuous slow currents of air generated by the 

 aspirators are then kept up, through these chambers, over 

 either surface of the leaf. In experiments on respiratory 

 exhalation, the current is freed from CO, by the potash 

 "tower" before it enters the chamber. Leaving the 



