124 



ROYAL HORTICULTURAL SOCIETY. 



stem. "We may therefore by manuring push the production of 

 fruit and flowers, in fruit-trees, to such an extent that they 

 will at last perish, especially in dry soils. I have myself seen 

 young pear- and plum-trees, in certain years, perish from over- 

 manuring. Gypsum never produces this effect, whereas if gypsum 

 operated by the fixation of carbonate of ammonia it must have 

 the same effect as animal manures. 



In my treatise ' On the Discovery of the Real Mode of Nutri- 

 tion in Plants,' I have thoroughly explained the operation of 

 gypsum, and illustrated it by experiments. It rests simply on 

 the supply of sulphuric acid and the assimilation of sulphur, 

 whereby the oxygen is carried off by respiration. The sulphate 

 of lime in the gypsum is not immediately appropriated by plants ; 

 but the abundant oxalic acid in leguminous plants sets the sul- 

 phuric acid free, since the oxalic acid, in consequence of its greater 

 affinity for lime, combines with it to form oxalate of lime. In the 

 older parts of the plant, therefore, as a residuum of this process, 

 large quantities of crystallized oxalate of lime are found, which 

 often fill the whole tissue. 



Thaer was aware that pure attenuated sulphuric acid sprinkled 

 on plants has the same effect as gypsum, which is easily explained 

 by the fact that gyj)sum itself oj>erates by means of the elimina- 

 tion of sulphuric acid by means of oxalic acid. Gypsum, there- 

 fore, has no effect on plants like grasses, which contain little or 

 no oxalic acid. This old experience is explicable only in this 

 manner. Exactly in the same way as gypsum, phosphate of lime 

 is decomposed by oxalic acid, and the phosphoric acid assimilated, 

 and exactly in the same way all other salts of lime, and amongst 

 them the humate. 



Were Liebig's theory true, that gypsum acts only by the fixa- 

 tion of ammonia, the effect on all plants must be the same, and 

 similar to that of animal manure ; in this case gypsum must be as 

 profitable a manure to meadows, rye and wheat crops, as to clover 

 and peas, which is, however, notoriously contrary to truth. 



The Liebigian theory of patent manures, which rests on erro- 

 neous views of the nutriment of plants by means of carbonate of 

 ammonia, and according to which a mixture of salts of potash and 

 soda with lime and magnesia is prepared with carbonate of 

 ammonia, has not been confirmed by its practical use, and the 

 sanguine hopes which were entertained by many in its favour 

 have been sadly deceived. Prince Dimitrii Dalgoroucki has in 

 consequence lost a whole crop of mangel wurzel in the South of 



