23 



discovery of M. Theod. de Saussure, that porous bodies, and 

 especially such as abound in carbon, possess the property of 

 attracting and compressing certain gases : thus, for instance, 

 carbon can absorb 9^ times its volume of oxygen. It is pos- 

 sible that the absorption of oxygen in plants takes place in 

 a similar way, at least the quantity of oxygen consumed coin- 

 cides with the number of stomata and air cavities in certain 

 plants. All porous bodies however do not possess this pro- 

 perty of compressing gases ; magnesia and lime for instance 

 are exceptions. 



The contents of the remaining portion of this work have 

 partly been published in earlier papers, and we have moreover 

 partially noticed the essential points in our last year's report*. 



Dr. Schleidenf has published some observations on the 

 luxuriant development of various plants in water containing 

 carbonic acid. The springs in the valley of Gottingen abound 

 in free carbonic acid, especially the basins near the Wehnder 

 paper-mill, and there is here found a rich and luxuriant vege- 

 tation, which in spring appears several entire weeks earlier 

 and continues in autumn much later than at other spots of 

 the same district. Dr. Schleiden thinks that the free carbonic 

 acid in the water exercises a favourable influence on the ve- 

 getation, which certainly may be the case ; for observations 

 have shown, that during the vegetation of plants in solar light, 

 the addition of a very small quantity of carbonic acid in the 

 surrounding atmosphere produces a much more powerful dis- 

 engagement of oxygen than takes place in the common atmo- 

 sphere. 



In the memoir on the soul of plants, M. v. Martius J has 

 stated his views on the nutrition of plants. The whole force 

 of vegetable life evinces itself most prominently in its indica- 

 tions of assimilation, as here inorganic matter must be con- 

 verted to organic, and have form given to it. This is an essential 

 character, in which plants differ from animals, as these for the 

 most part take up only organized nutriment. The plant, says 

 M. v. Martius, derives its nourishment from the earth, the 

 water, and the atmosphere ; but I think I am able to prove 



* See Lond. and Edinb. Philosophical Magazine, vol.xi. p. 536. 



f Notiz iiber die Einwirkung freier Kohlensiiure auf die Ernahrung der 

 Pflanzen. Wiegmann's Archiv, p. 279, 1837 ; and Annals of Nat. Hist. p. 

 235. No. IX. 



I Reden und Vortrage, &c., p. 244. 



