168 Presents. [Dec. 6, 



amount which diffuses through is estimated. On supplying 31 per 

 cent. C0 2 to the lower surface of a leaf of Nerium. only O035 per 

 cent, appears by diffusion in a slow current of air kept continually 

 passing over the upper surface of the leaf. 



Other experiments on the respiration of injected leaves also support 

 the view that the stomatal openings, in spite of their minuteness, 

 offer a very much easier path from the atmosphere to the interior of 

 the leaf than does the cuticle. 



Conclusions. 1. Under normal conditions practically the sole path- 

 way for C0 2 into or out of the leaf is by the stomata. Since oxygen 

 diffuses more readily than C0 2 through fine openings, the same prob- 

 ably holds for oxygen and the whole of the gas exchange. .. 



2. Under abnormal conditions, when the stomata or intercellular 

 spaces are blocked and the surrounding tension of C0 2 is great 

 enough, passage of C0 2 by osmosis through the cuticle may take 

 place. 



3. That such closure of stomata as is held to take place in darkness 

 does not prevent the distribution of gas exchange closely agreeing 

 with that of the stomata. 



4. That the exhalation of C0 2 in bright light by a leafy shoot in 

 Garreau's well-known experiment is not the expression of any phy- 

 siological truth for the leaf, but only due to the imperfections of the 

 conditions ; to the presence of immature parts, or of tissues not suffi- 

 ciently green or not fully illuminated. Mature isolated green leaves 

 fully illuminated assimilate the whole of their respiratory C0 2 and 

 allow none to escape from them. 



Presents, December 6, 1894. 

 Transactions. 



Boston : American Academy of Arts and Sciences. Proceedings. 



Vol. XXIX. 8vo. Boston 1894. The Academy. 



Brisbane: Queensland Branch, Royal Geographical Society of 



Australasia. Proceedings and Transactions. Vol. IX. 8vo. 



Brisbane 1894. The Branch. 



Cambridge, Mass. : Museum of Comparative Zoology. Bulletin. 



Vol. XXV. STos. 910. 8vo. Cambridge 1894. 



The Museum. 

 Cracow: Academic des Sciences. Bulletin International. Octobre, 



1894. 8vo. Cracovie. The Academy. 



Dublin: Royal Irish Academy. Transactions. Vol. XXX. Parts 



1314. 4to. Dublin 1894. The Academy. 



Edinburgh : Botanical Society. Transactions and Proceedings. 



Vol. XX. Part 1. 8vo. Edinburgh 1894. The Society. 



