80 ANATOMY AND PHYSIOLOGY OF 



otliers require a mixed food, and, finally, to the parasites are 

 assigned solely the still undecomposed saps elaborated by other 

 plants. 



Ohserv. From such experime^its made in the rough, of course no 

 accurate bcientific result can be deduced, these can be derived only from 

 experiments carefully made upon a small scale. "We are by no means 

 without experiments on a small scale of this soi^t, but unfortunately 

 most of them have been made in a manner which renders them incapa- 

 ble of furnishing any useful result. To these belong all earlier attempts 

 to grow plants with distilled water, or water containing carbonic acid, in 

 &and, pieces of marble, (fee, in which plants of course would not flourish, 

 but from which no conckision can be drawn, since not merely the organic 

 matters, but all the earths, salts, ko., which they required, were with- 

 drawn from the plants. In order that these experiments sliould furnish 

 any certain result, they woidd require to be made in such a way, that the 

 same species of plant would be grown in a soil wliich contained organic 

 substances, and in artificial mixtures wliich contained all the inorganic 

 constituents of the fertile soil, without the adinixture of any organic 

 constituents. In respect to this, Wiegmann, at my suggestion, made 

 experiments {'' Bot. Zeit,'' 1843, 801), according to which, plants raised in 

 soil devoid of humous grew very poorly and mostly soon died. Mulder 

 made a larger series of analogous experiments (" Fhys. Clmnr\ which like- 

 wise lead to the belief in the use of the organic substances contained in 

 arable soil, as well as of the humic acid and ulmate of ammonia arti- 

 ficially added to it. 



Even if* these experiments were still far from having decided the ques- 

 tion of the necessity of organic food in a definitive manner, the results are 

 so very concordant with those of experience on a large scale, that there 

 can be no doubt of their general correctness, the more, that these expe- 

 riments made on the smallest scale, obtain a confirmation through the 

 extraordinary small results which manuring with Liebig's solely inorganic 

 manures has everywhere had, when comparative experiments have been 

 made. Instead of reforming agricultui-e by his manures, Liebig has 

 caused them to demonstrate the incorrectness of his theory of the nutri- 

 tion of vegetables. 



Yet the humous substances in vegetable mould, do not derive their im- 

 portance to plants from an immediate applicability as food, but exercise 

 their great influence on plants principally through their relations with 

 the alkalies and earths, and especially with ammonia. I shall take the 

 liberty of giving some of the principal results of Mulder's researches, 

 since these open out a series of new points of view, which promise to 

 become of the greatest importance to the theory of vegetable nutrition. 

 According to these investigations, the substances beginning to undergo 

 decomposition in the earth are gradually converted into a series of 

 chemical compounds, first into ulmine, then into ulmic acid, humin, 

 humic acid, geic acid, apocrenic, and finally into crenic acid. With the 

 exception of the first and third, these compounds* play the part of acids, 

 and combine in the soil with its alkalies and earths. These acids, con- 

 taining no nitrogen, possess a particularly strong affinity for ammonia, 

 which is always met with, more or less abundantly, in combination vdth 

 them. The compounds of these acids with alkalies are readily poluble 



