ZOOLOaY AND BOTANY, MICKOSCOPY, ETO. 275 



potassium and. sodium in the vegetable organism, setting tlie hydro- 

 chloric acid free. The free hydrochloric acid he believes to play an 

 important part in the vital economy, in the formation of starch by 

 means of diastase. 



Source of the Nitrogen in Plants. — In the experiments con- 

 ducted at Eothamsted, Sir J. B, Lawes has paid great attention to 

 the question of the source of the nitrogen contained in the tissues of 

 plants. He confirms the ordinary view that the atmosphere is, if not 

 the sole, at all events the chief source of the carbon in plants, and 

 that the soil is the principal, if not the only source of their nitrogen. 

 The veiy small amount of nitrogen brought down to the soil from the 

 atmosphere by rain in the form of salts of ammonia is not of itself 

 sufficient to afford the requisite quantity of nitrogen to plants 

 directly ; this must be looked for rather in the nitrates present in the 

 soil and in manures. The different results of different modes of treat- 

 ment on different plants are due to the difference in the natm-e of the 

 roots as to extent, thickness, &c., and as to their capacity to draw 

 moisture from superficial or from deeper-lying strata of the soil ; and 

 to their different capacities to set free the nutrient substances and to 

 assimilate. Although a leguminous crop, like clover, removes a much 

 larger quantity of nitrogen from the soil than a cereal crop, a much 

 better crop of wheat will nevertheless be obtained from the same soil 

 after a crop of clover than after a crop of rye. The clover has 

 obtained the nitrogen from a greater depth in the soil, and the roots 

 and other portions of the clover crop that still remain in the soil, 

 yield to the wheat a much larger quantity of nitrogen than the 

 superficial stratum of soil would do. 



Formation of Nitrates in Plants.* — Berthelot and Andre have 

 investigated the source of the potassium nitrate which is found in 

 large quantities especially in certain plants, as Borrago and the 

 Amaranthacese. It occurs in the largest quantity in the stem, next in 

 the root, to the smallest extent in the secondary roots and flowers, and 

 least of all in the leaves. The percentage and absolute quantity of 

 potassium nitrate in the plant gradually increase from the period of 

 germination, attaining their maximum immediately before the time of 

 flowering. From this time its relative proportion declines, a portion 

 of the nitrogen being used up in the formation of the protein- 

 compounds which are required for the seed, for which purpose a portion 

 of the nitrate is decomposed. To a certain extent there may be con- 

 sidered to be an antagonism between the production of nitrates and the 

 process of assimilation which takes place in the green parts of plants. 



With regard to the source of the nitrates, the authors are of 

 opinion that plants do not derive them directly either from the soil, 

 from manures, or from the atmosphere ; but that they are formed in 

 the plant itself and especially in the stem. Experiments at Mont- 

 souris show that the amount of nitric acid which can be obtained from 

 the atmosphere corresponds to only 4*4 kilogrammes of potassium 



* Comptes Rendus, xcis. (18S4) p. 683. 



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