Reviews. — Liebig^s Organic Chemistry. 347 



Chapter II. treats of the assimilation of carbon, in a full 

 and interesting manner, and details many facts of surprising 

 beauty, relative to physiological topics. As the subject of 

 carbon, in reference to its adaptation to horticultural purpos- 

 es, is now under favorable notice among our florists and ama- 

 teurs, we select as follows: — 



How does it happen, it maj- be asked, that the absorption of car- 

 bon from the atmosphere by plants is doubted by all botanists and 

 vegetable physiologists, and that by the greater numlier the puritica- 

 tion of the air by means of them is wholly denied? 



These doubts have arisen from the action of plants on the air ia 

 the absence of light, that is, during the night. 



The experiments of Ins-enhouss were in a great measure the cause 

 of this uncertainty of opinion, regarding the influence of plants in 

 purifying the air. His observation, that green plants emit carbonic 

 acid in the dark, led De Saussure and Grischow to new investiga- 

 tions, by which they ascertained that under such conditions plants do 

 really absorb oxygen, and emit carbonic acid ; but that the whole 

 volume of air undergoes diminution at the same time. From the lat- 

 ter fact it follows, that the quantity of oxygen gas absorbed is 

 greater, than the volume of carbonic acid separated ; tor if this were 

 not the case, no diminution could occur. These facts cannot be 

 doubted, but the views based on them have been so false, that noth- 

 ing, except the total want of observation, and the utmost ignorance 

 of the chemical relations of plants to the atmosphere, can account for 

 their adoption. 



It is known, that nitrogen, hydrogen, and a number of other gases, 

 exercise a peculiar, and, in general, an injurious influence upon liv- 

 ing plants. Is it then, probable, that oxygen, one of the most ener- 

 getic agents in nature, should remain without influence on plants 

 when one of their peculiar processes of assimilation has ceased? 



It is true, that the decomposition of carbonic acid is arrested by 

 absence of light. But then, namely, at night, a true chemical pro- 

 cess commences, in consequence of the action of the oxygen in the 

 air, upon the organic substances composing the leaves, blossoms, and 

 fruit. This process is not at all connected with the life of the vege- 

 table organism, because it goes on in a dead plant exactly as iu a liv- 

 mg one. 



The substances composing the leaves of diflferent plants being 

 known, it is a matter of the greatest ease and certainty, to calculate 

 which of them, during life, should absorb most oxygen by chemical 

 action, when the influence of light is withdrawn. 



The leaves and green parts of all plants, containing volatile oils or 

 volatile constituent! in general, which change into resin by the ab- 

 sorption of oxygen, should absorb more than other parts w hich are 

 free from such substances. Those loaves, also, which contain either 

 the constituents of nut-galls, or compounds, in which nitrogen is 

 present, ought to absorb more oxygen than those which do not con- 

 tain such matters. The correctness of these inferences has been dis- 

 tinctly proved by the observations of De Saussure: for, whilst the 



