SCHULTZENSTEIN — NUTRITIVE CONSTITUENTS OF WATEE. 133 



contain humous extract, since by evaporation they give a dark- 

 brown residuum. 



On the other side, Liebig was not aware that the colourless sap 

 of such trees as birch and maple yields a brown humous residuum 

 when evaporated, as I have proved by experiment. The brown 

 tint, therefore, of humous extract is no argument against its imbi- 

 bition from water. 



The humous extract imbibed, together with humic acid and per- 

 humates, forms the foundation for the formation of dextrine and 

 sugar in raw sap, whence the gum is transformed into sugar. The 

 dextrine is therefore, at first, of a humous brown, as also grape- 

 sugar. The formation of all the constituents of sap out of the 

 humous particles dissolved in surface-water and river-water, which 

 may be regarded as belonging to the same category as the bitu- 

 minous particles in the older alpine formations, and in consequence 

 the process of nutrition, may therefore be regarded as incontest- 

 able. The further development of these constituents into vital 

 sap, has been followed out by us in our treatise ' On the Discovery 

 of the Mode of Nutrition in Plants,' through observations on the 

 respiration of plants, according to which the oxygen given out 

 does not arise from the decomposition of carbonic acid, but simply 

 from the decomposition of the hydrated vegetable acids, or the 

 mineral acids containing sulphur and phosphorus. All this was 

 inexplicable according to the earlier notions on the nutritive 

 power of humtis, while the facts which have been detailed were 

 unknown. This was the cause of the value ascribed to the carbonic- 

 acid theory, and of the practice of manuring in gardens and in 

 the fields being so perplexed ; so that it was a matter of absolute 

 necessity in behalf of agriculture and horticulture to get rid of 

 the errors of this theory ; while it is a subject of regret that, in 

 botanical teaching, theories the most contrary to nature and in 

 contradiction to all practical experience, and leading only to 

 botanical perplexity, should be preferred. It was necessary to 

 show previously that it is not the air, but the water alone, which 

 conveys nourishment — that the nutritive matter is dissolved in 

 water, by means of which it preserves its nutritive powers — and 

 how it works. 



The observations of the long- sustained vegetation in many 

 succulent plants, as Sedum, Epidendrum, Tradescantia, are very 

 deceptive as regards the carbonic -acid theory and the nourish- 

 ment of plants from air. Such plants when hanging in the air, 

 while the pots are unwatered, flourish only after having first 



