554 



Miscellaneous. 



this question is settled may be made every day. It will be found 

 that a plant in a pot dies if it is not watered, that in the open 

 ground it continues to live for a considerable length of time without 

 rain, because the soil continually absorbs the watery vapours of 

 the atmosphere, especially during the night ; but that when drought 

 continues for a long period, plants growing in the open country 

 suffer, especially because the drought diminishes the capacity of the 

 liumus for absorbing moisture (Mitscherlich). These facts are 

 known to every peasant, to every gardener, but as it seems, are 

 unknown to Dr. Liebig. 



To prove the absorption of carbonic acid by leaves, the author ap- 

 peals to the well-known experiments of Saussure. According to 

 the same experiment, he is obliged to admit that they emit carbonic 

 acid at night ; but he asserts, without any kind of proof, that this 

 carbonic acid is derived from a quite different source, and that 

 the quantity thus emitted is not equal to that which has previously 

 been absorbed. But since the experiments of Saussure, Link, and 

 Grischow, according to which, plants vegetating in an air, to which 

 that of the atmosphere has not access, do not change the air in its 

 qualitive or quantitive relations, have not been reported by Dr. 

 Liebig, I shall take the liberty to oppose these well-conducted and 

 exact experiments, to the phrases of Dr. Liebig, and I think I may 

 assert that in this matter there is still a great vacuum in our know- 

 ledge, to fill up which this author does not seem better qualified 

 than physiologists. 



Meyen being aware of these difficulties, was nearly the first and 

 only physiologist to deny that the atmosphere is improved by the 

 functions of the leaves, and he has proposed a theory, resting, 

 indeed, on a very weak foundation. Now Dr. Liebig asserts (p. 24,) 

 that in the writings of all vegetable physiologists and botanists, the 

 assimilation of the carbonic acid of the air is called in doubt, and 

 that most of them deny that the air is improved by plants. This is 

 another proof of his great ignorance, or rather gross falsification of 

 historical data known to every body, and it is not worth my while to 

 answer them more fully. 



Dr. Liebig, after having (p. 26) enumerated a number of single 

 well-known facts,, which have produced in his mind the certain 



