466 Ml:. .1. B. LAWES, DR. GILBEET, AND DB. PI OH 



in sunlight was in 1 1 1 : 1 1 1 \ ca i ozonou . He aspirated a large quantity of air. in the 

 neighbourhood of vegetation, through carded cotton, and then through sulphuric acid, 

 to wash it. The washed air then pas i-d over potassium, and through a dilute solution 

 of pure potash, when nitrate of potash was formed. When, on the other hand, air in 

 the mid .1 of habitations was operated upon in a similar way. the formation of nitric 

 acid was not observed. M. de Luca supposes the air surrounding vegetation, in sum- 

 light, to be o/onous; that by its moans the Nitrogen of the air may be converted into 

 nitric acid; and that thus the Nitrogen of the air maj be rendered available for assimi- 

 lation bv plants, under the influence of vegetation itself. 



G. — Tin: Experiments of M. Hasting*. 



In 1855, M. Harting published some criticisms, and the results of some experim< 

 on the question of the assimilation of Nitrogen by plants. He considered that the 

 Nitrogen of the air might contribute indirectly to vegetation. Ho attributed a for:; - 

 tion of ammonia from the decomposing debris of seeds. &c, and the free Nitrogen of 

 the air, in the case of M. Ville's experiments ; and also supposed that nitric acid 

 might be formed by- the oxidation of the atmospheric Nitrogen. The increase of Nitro- 

 gen in M. Ville's plants, and of ammonia in the water of the enclosing apparatus, was 

 taken as proof of such formation of ammonia. 



M. Harting made two sets of experiments, in one of which the plants grew in a limited 

 volume of air, and in the other in a current of air washed free from ammonia — both 

 arranged with a view to avoid the formation of ammonia. He employed enclosing-appa- 

 ratus somewhat on the plan of M. BoussiNGAULT and M. Villi: ; but he used gL ss \ases, 

 instead of porous pots, for his plants. He grew Beans, Buckwheat, and Oats. After 

 the seeds had germinated, and the plants had protruded a little above the surface of the 

 artificial soil, he covered the latter wdth a mixture of wax and oil, to shut off the ae< 

 of air. He further enclosed the stems of the plants in caoutchouc tubes ; and inserted 

 other caoutchouc tubes through the waxy coating, for the supply of water. Some of the 

 plants were very vivacious at first; and in the case of the Beans, two began to flower; 

 but then the leaves turned yellow, and the experiment was stopped. His apparatus 

 consisted of tinned-iron pans, varnished, and surmounted by glass shades of IS litres 

 capacity. There was an aperture for the admission of carbonic acid, another for that of 

 water, and so on. 



The result was that the produced plants yielded no more dry matter than was con- 

 tained in the seeds. M. Hasting considered, therefore, that the determination of the 

 Nitrogen was superfluous. The growth evidently stopped when the supplies of the seeds 

 were exhausted. M. Harting's general conclusions on the subject were as follow : — 



1. Plants absorb salts of ammonia, and nitrates, by their roots. 



2. The Nitrogen of the air contributes to the formation of ammonia, and nitrates, in 

 the soil. 



3. It is not proved that Nitrogen serves directly for the nutrition of plan. s. 



* Couipt. Rend. sli. 1855. 



