92 Dr. Hugo Mold, on Liebig s Organic Chemistry, 



organs, a position fully borne out by recent microscopical experi- 

 ments on the formation of the cellular tissue in plants. If this is 

 the case, we may also assume that the formation of substances 

 nearly related to woody fibre, such as sugar, gum, and starch, re- 

 quires also a certain amount of nitrogen ; and that a less amount, 

 although it may suffice for the abundant formation of those sub- 

 stances, will only produce a small amount of woody fibre, is an 

 opinion adopted by Liebig. It may be also assumed, that if such an 

 amount of nitrogen as is sufficient for the formation of a moderate 

 quantity of woody fibre, is to be divided between the formation of 

 gum and other similar substances (composed of carbonic acid and 

 water,) and that of woody fibre — the same amount of nitrogen might 

 suffice for the formation of a greater amount of woody fibre, and 

 therefore, for the more vigorous growth of the plant ; in those cases 

 where the plant has already absorbed part of its food in the form of 

 substances, which (being composed of carbonic acid and water) have 

 also attained the first degree of vegetable assimilation. 



Liebig believes, that, in this case, the function of the leaves will be 

 impaired. This, however, it is impossible to decide, "as we have 

 not even an idea of the variations which the assimilative process 

 may undergo, according to the difference of the substances on which 

 plants feed. It is also, in most cases, less essential to know whether 

 plants absorb only organic substances and water, than whether it is 

 necessarily in conjunction with inorganic matter, that such ab- 

 sorption takes place ; in which case, the digestion (Verarbeitung) of 

 inorganic substances would not be suspended ; but, in conjunc- 

 tion with this assimilative process, another and different one would 

 make its appearance." To decide on the existence of these pro- 

 cesses, it would be necessary to know the metamorphoses which food 

 undergoes in plants. But this is not the case, as we neither 

 are aware of the manner in which gum or sugar are formed, nor of 

 the further changes of these substances into woody fibre. Chemis- 

 try, it is true, can change wood and starch into sugar, but only by 

 the application of strong chemical agencies, which we know are not 

 made use of by plants. To imitate the real process is beyond 

 the reach of chemistry ; still, it is to this very process that plants 

 owe their growth. Under such circumstances, all that we can do is 



