ORTGIN OF THE NITROGEN. 29 1 



where of course it only occurs in very small quantity, also presents no difficulty 

 ■with respect to its origin : we added it in fact to the nutritive solution in the form of 

 calcium and magnesium sulphates, and if we now find it also in the proteid sub- 

 stances of the protoplasm of our plants, no longer in the form of sulphuric acid 

 but as an elementary constituent in the formula of proteid substance, there is little 

 to be surprised at, since we know how easily sulphur compounds may be 

 decomposed. We also find in the micro-chemical investigation of our plants, as 

 a residuum of this decomposition, crystals of oxalate of lime, the calcium of which 

 passed into the plant in the form of calcium sulphate. 



Of the elements of which protoplasm, cellulose, and the other organic com- 

 pounds produced by the plant consist, the nitrogen and carbon still remain to be 

 considered. Our table (p. 284) shows that in the water of the nutritive mixture, a 

 salt containing nitrogen, viz. potassium nitrate, is contained, and indeed predominates. 

 The nitrogen in the proteid substances of the plant is, as we may thus assume, 

 the same nitrogen which we presented to the roots in the form of saltpetre. On 

 the decomposition of this salt, its nitrogen must have become a constituent of the 

 proteid substances newly produced in the plant. At any rate the active vegetation 

 of our experimental plants, and the very significant increase of substances of a proteid 

 nature which had been especially stored up in the gathered seeds, show that plants 

 are able to take up from nitrates as much nitrogen as is necessary for the formation 

 of the proteid substances of a vigorous plant. 



Theodore de Saussure had already proposed the question whether the nitrogen 

 of the atmosphere (which, as is well known, consists of about ^ nitrogen and \ oxygen) 

 is not used by plants to produce their nitrogenous compounds. Thirty or forty 

 years ago Boussingault endeavoured to decide this question by a long series of 

 exceedingly careful experiments on vegetation, and came to the conclusion that 

 the atmospheric nitrogen is not employed in the process of the assimilation of 

 plants. His experimental plants in each case grew vigorously and produced proteid 

 compounds when he presented to their roots, in addition to the other nutritive sub- 

 stances, various kinds of nitrogenous compounds. They grew, on the other hand, 

 very badly, and their proteid substances did not increase, when such a supply 

 of nitrogen compounds was wanting ; although the nitrogen of the atmosphere 

 was at the disposal of the plants so treated. By means of the now much further 

 developed art of nourishing plants artificially, and especially by means of water- 

 cultures, we are in a position at any time to afford ocular demonstration of 

 the important result obtained by Boussingault, by means of simple experiments. 

 Whenever a sufficient quantity of saltpetre is added to the nutritive solution, the 

 experimental plants grow vigorously, produce numerous ripe seeds capable of 

 germination, and give on analysis a corresponding increase of the nitrogenous 

 substance. If on the other hand the nitrate is withheld from the nutritive mixture, 

 the experimental plant continues to grow for a time, it is true, making use of the 

 proteid substances already contained in the seed for the formation of the protoplasm 

 of its organs ; and this stunted growth may even continue for some time, since the 

 protoplasm of the first leaves is again dissolved and absorbed from them, to be 

 employed for the formation of a few new leaves ; but even in this case analysis 

 gives no increase of the proteid substances. 



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