BOTANY. 783 



mucli may bo <;i\<'n oil' Iroin the lower stomatiferous surface. When 

 stomata occur on both surfaces the rehitive amounts of the gas exhaled 

 closely follow the ratios of tlie uiimber of stomata. To prove this the 

 author shows that Ampelopsis hederacea^ with no stomata on the upi^er 

 surface, hut with many on the lower, exhales carbon dioxid in the 

 l)ro])ortion <»f .'3:100 for tlie tw^o sides; in Allsnia pkoiUtf/o the proportion 

 of the stomata on the two surfaces is as 135:100, and the proportion of 

 the gas exhaled is as 120:100; in Iris (/I'muoiica, with an equal number 

 of stomata on each surface, the pro]>ortion of tlie gas exhaled by the 

 two surfaces is as 110:100; and in Rlcinus communis the proportion of 

 stomata is as 100:250, and the gas exhaled is as 100:260. 



Experiments in the absori)tion of carbon dioxid during assimilation 

 showed the same close relation to the distribution of stomata. As 

 hitherto carried out, the author considers direct sunshine, continuous 

 for several hours, as essential to the success of these experiments. A 

 very simjjle experiment of the author's will show that the stomata are 

 practically the sole path of entry of carbon dioxid for assimilation. If 

 part of the lower stomatic surface of any leaf^ having no stomata on 

 its upper surface, be coated with wax so as to mechanically block the 

 stomata, no starch can lie formed in that area, while adjacent areas 

 may become rich in starch. 



The previously mentioned experiments by Koussingault were con- 

 ducted with the leaves of Neriioii oleander, the upi)er surface of whose 

 leaves possesses no stomata. These leaves assimilated less when the 

 upper surface had been coated with wax than when the lower stoma- 

 tiferous surface had been so coated. The author claims that the expla- 

 nation of this is due to the fact that Boussinganlt experimented with 

 the leaves in an atmosphere containing 30 per cent of carbon dioxid, 

 which is greatly in excess of the o])tiinum percentage of carbon dioxid 

 asi^imilated by this leaf. Under these conditions there penetrates into 

 the leaf so much of the gas that its assimilatory activity is lessened 

 and falls below that of another leaf, into w^hich, owing to the blocking 

 of the stomata, the gas diffuses very slowiy and can not exceed the 

 optimum strength. 



Further evidence on the possible paths of gaseous exchange has been 

 obtained by investigating the degree to which diffusion of carbon 

 dioxid can be artificially produced through the living- leaf. Strong- 

 mixtures of the gas were led continuously across one surface of the 

 leaf and the amount which diffused through it w^as estimated. Other 

 experiments on the respiration of injected leaves also support the view 

 that the stomata! openings, in spite of their minuteness, offer a much 

 easier path from the atmosphere to the interior of the leaf than does 

 the cuticle. The conclusions of the author are as follows : 



"(1) Under uoniial conditions practically the sole pathway for carbon dioxid into 

 or out of the leaf is by the stomata. Since oxygen diffuses more readily than car- 

 bon dioxid through fine openings, the same probably holds for oxygen and the whole 

 of the gas exchange, 



