Mr. F. F. Blackman. Experimental Researches [Dec. 6, 



pose, shallow capsules 10 sq. cm. in area, consisting of a glass plate 

 with a metal rim, through which tubes for the circulation of the air 

 current pass, are employed. Two of them are affixed to a leaf on 

 opposite sides of the same area in air-tight union by means of soft 

 wax. Then, in the way described previously, two continuous currents 

 of air can be kept up over the two surfaces, and the C0 3 produced 

 or taken in, during a given time, by each of them be determined. 



Numerous experiments on the respiration of a variety of leaves, 

 thick and thin, with the stomata all on the one side or with stomata 

 variously distributed on the two sides, agree in showing that the 

 stomata are the site of the exhalation of this gas. When no stomata 

 are present on the upper surface of a leaf, then practically no CO 2 is 

 exhaled from that surface, at least, not more than falls within the 

 working error of the apparatus under these conditions, while more 

 than thirty times as much may be given off from the lower stomati- 

 ferous surface. When stomata occur on both surfaces, the relative 

 amounts of C0 2 exhaled closely follow the ratios of the numbers of 

 stomata. 



A few examples in illustration of this may be given. 



Column A gives the proportionate numbers of stomata on the two 

 surfaces ; B the amounts of C0 2 exhaled by these ; C the ratios of 

 these amounts. Each experiment lasted about fifteen hours. 



Experiments on the absorption of C0 2 during assimilation showed 

 the same close relation to the distribution of stomata. For these 

 experiments a constant fixed amount of C0 2 must be introduced into 

 the air stream supplied to the leaf, which makes them much more 

 complicated. 



As hitherto carried out, direct sunshine, continuous for several 

 hours, has been essential for the success of these experiments. They 

 are, consequently, but few in number, though perfectly clear in their 

 interpretation. 



