256 APPENDIX TO PART I. 



Splendidly, and remain the whole summer green, even in 

 the greatest heat. 



" 'All my neighbors wonder very much how my vine- 

 yard is so rich, and that I obtain so many grapes from it, 

 and yet they all know that 1 have put no dung upon it for 

 ten years.' ""^ 



KOOT SECRETIONS. 



It should be stated, that the accuracy of the experiments 

 of Macaire-Princep adduced by the author, page 164, is 

 not generally admitted. Other chemists have been unable 

 to obtain similar results, or if they do are inclined to as- 

 cribe them to injury of the roots of the plants examined. 

 Professor Lindley in his notice of Liebig's work has re- 

 marked, that he has no fixed opinion on the subject, it 

 being a question of facts and not of induction. Admitting 

 root secretions, he nevertheless does not deem it necessary 

 to look to the roots for these excretions, when we have so 

 many proofs of their constant occurrence in other parts of 

 a plant, as in the oily, resinous, waxy, acid, and acrid mat- 

 ter, from various parts of their surface, and in the peculiar 

 substances lodged in the hollows of their stems or elsewhere, 

 such as Tabasheer, in the bamboo. These are thought to 

 be instances, "sufficient to satisfy the necessity of excre- 

 tions occurring, and to render it superfluous to look to the 

 roots for further aid in this particular." 



The subject of excretion is one of great interest, and 

 deserving of further examination. Several botanists have 

 recently stated what are deemed fatal objections to the cor- 

 rectness of De Candolle's conclusions from Macaire's ex- 

 periments. It is maintained, that the process of excretion 

 from the roots of plants is not analogous to that of excretion 

 in animals ; that the deposits consist of materials which 

 were in superabundance in the system of the plant, and 

 that the reason why the same species of plants do not grow 

 one after the other, is, that the first exhausted the soil of 

 the materials necessary for the nourishment of the next. 

 In some parts of the world, wheat crops are said to have 

 been obtained fifty years in succession, where the supply 

 of nutriment was sufficient. The application of the recent 

 discovery of the means of coloring the wood of trees by 



* The e.^periment has been made here with success — fV. 



