CH. IT. 



COURSE OF THE SAP. 



49 



pot-plants are not watered, even in our moist English 

 summer, their roots would have nothing to imbibe 

 from, and the plants would die. What faith is the 

 practical man to place in the theorist who puts him up 

 to such secrets as these ? Possibly Liebig may have 

 taken his vegetable physiology on trust from others ; 

 but certainly this is one of a dozen monstrous theories 

 with which this (so said) profound chemist would 

 annihilate the very foundations of vegetable physiology, 

 giving him the best. ' Mutato nomine,' his own words 

 to Burdach apply to Liebig : ' All inquiry is arrested 

 by such opinions, when propagated by a teacher who 

 enjoys a merited reputation obtained by knowledge 

 and hard labour.' 



Liebig writes, in reference to ferns, &c. : ' They 

 resemble in this respect the plants which we raise 

 from bulbs and tubers, and which live, while young, 

 upon the substances contained in their seed, and require 

 no food from the soil when their exterior organs of 

 nutrition are formed. This class of plants is even at 

 present ranked amongst those which do not exhaust 

 the soil.' According to this, we ought to be able to 

 grow our potatoes without any soil at all : but, in fact, 

 there is no crop which exhausts the soil for itself more 

 than potatoes ; there is no crop which is more grateful 

 for a change of soil ; and there is no crop whose 

 growth differs more, according to the different soil in 

 which it is grown. Any one of these three facts proves 

 that the potato is nourished from the soil^ not from the 



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