272 ANNUAL OF SCIENTIFIC DISCOVERY. 



ammonia by means of their leaves. This property renders these plants valu- 

 able in agriculture. Grains in general, those of natural meadows and cereals, 

 do not absorb carbonate of ammonia by means of their leaves, they only ab- 

 sorb it in a state of solution by means of their spongioles. 



The nitrogen of the air is not absorbed by the aerial organs of plants, but 

 the nitrogen dissolved in water, which penetrates into plants by means of 

 then* roots, is assimilated. This explains the contradictory statements of MM. 

 Boussingault and Yille as to the assimilation of nitrogen. A plant placed in 

 a limited atmosphere, which thus accomplishes all the phases of its develop- 

 ment, does not transpire water by means of its leaves. It follows that it only 

 absorbs a limited quantity of water by means of its roots, and consequently 

 an inappreciable quantity of nitrogen. 



Plaster produces a direct and marked effect only on plants which absorb 

 carbonate of ammonia in a gaseous state that is, by means of their leaves ; 

 such are the leguminous plants of artificial meadows, lucerne, etc. The effect 

 of plaster is to cause the absorption by the leaves of the carbonate of ammonia 

 which the dew and rain bring to the surface of the earth and plants. During 

 the last stage of decomposition of manures, the nitrogen is disengaged from 

 the soil in the state of carbonate of ammonia. The dew brings it back upon 

 the plants, moistening their surfaces and obstructing their respiratory organs. 

 In these conditions the carbonate of ammonia can not be absorbed. It is 

 disengaged among the first products of the vaporization of the dew before the 

 stomates are dried. The presence of plaster in the soil and on the plants has 

 this effect: 1st, of fixing the ammonia in the dew in a stajte of sulphate, and 

 forming, at the same time, carbonate of lime ; 2d, under the influence of a 

 continued vaporization, when the organs of plants are not moistened, the 

 sulphate of ammonia, which is not volatile in the presence of carbonate of 

 lime, causes a slow disengagement of carbonate of ammonia to the organs of 

 absorption, and the re-formation of sulphate of lime. Tin's latter thus acts 

 indefinitely. 



Plaster and the leguminous plants on which it acts consequently aid in 

 enriching nitrogenous manures ; it is to this enriching that I attribute generally 

 the potato disease. The careful study of this matter has shown that the 

 disease which destroys the potato is due to the absorption of carbonate of 

 ammonia by the roots of the plants. There is an elaboration of the nitrogen 

 in fermentation in the superior organs, an accumulation of this matter in the 

 tuber whence all the symptoms and manifestations of the disease. I have 

 proved the correctness of this conclusion by causing the absorption of car- 

 bonate of ammonia by some roots, which became thus inoculated, if I may 

 use the term, with the malady in different degrees. Comptes Rendus. 



INDIRECT MODE OF DETERMINING THE PRESENCE OF PHOS- 

 PHORIC ACID IN ROCKS. 



At the last meeting of the British Association, Dr. Daubeny gave an account 

 of a new method adopted by him for indirectly determining the presence of 

 phosphoric acid in rocks, and of obtaining proofs of its existence in the Silurian 



