5'46 



THE SOITTIIEIIN PLANTER. 



originally present in the seeds. They 

 were freely exposed to the atmosphere, 

 but they were incapable of extracting from 

 the atmosphere sufficient nitrogen to do 

 much more than to keep them alive. The 

 plants, however, in the brick-dust and 

 sand, to which not only phosphate of lime 

 but nitrate of potash had been added, 

 grew between three and four feet high, 

 and were equally high, and were as 

 heaithy and fertile as plants grown in a 

 rich garden soil. As an instance of the 

 vital powers of the different plants, I may 

 cite some figures. The plant in brick- 

 dust and sand alone produced, taking 

 the seed as one, a dry product of little 

 more than three parts ; while the one with 

 nitrate of potash and phosphate of lime 

 produced 198 parts ; and that of the phos- 

 phate of lime and carbonate of potash 

 about four parts. The plant in the nitrate 

 of potash showed 200 times the quantity 

 of nitrogen existing in the others. The 

 result of the nitrogen present in the plant 

 was shown also in the quantity of carbon 

 fixed in the tissues — the j-ubstance of 

 which the solid structure of the plant is 

 chiefly built. The carbon fixed in the 

 plant grown in the brick-dust amounted 

 to little more than the 1^ grain ; in the 

 plant grown with the nitrate of potash it 

 art)ounted to 120 grains, or eighty times 

 the former. The carbonic acid, which was 

 decomposed in twenty-four hours by the 

 starved plant, was only 2-| cubic centime- 

 tres : while that fed upon nitrate of pot- 

 ash coijsujoed in the same time 182 ; show- 

 ing that the presence of nitrogen in the 

 ma(nure was that substance which not only 

 produced the development, but produced 

 the increased quantity of nitrogen in the 

 product and the fixation of the carbon. 

 These experiments, physical and chemical, 

 bring the evid».-nce from one side of the 

 question to complete the reasoning fur- 

 nished by the anatomical conclusions to 

 which I previously alluded. The results 

 are remarkable in the two cases. Bous- 

 singault's experiments shew that nitrogen 

 is the efficient agent in the assimilation of 

 food, and the anatomical examination of 

 the tissues demonstrates the actual pro- 

 cess of elaboration taking ]»lace in the 

 midst of these nitrogenous substances. 



I'here are one or two other points to 

 which I must briefly advert, as of inter- 

 est in reference to this matter. I may 



mention, in tlie first place, that we have 

 lately had a new hypothesis as to action 

 of roots from Liebig, which, however, can 

 only apply to roots of a certain kind, and 

 not at all to those growing in water or 

 very wet soils. He has formed the sup- 

 position that roots act not merely by ab- 

 sorption of solutions, but by decomposing 

 solid substances with which they come in 

 contact. In this he endeavours to explain 

 the abstraction from soils of substances 

 apparently insoluble. He finds that not 

 only do aluminous soils, as shown by Prof. 

 Way, fix various useful substances, and 

 prevent their filtering through, but that 

 humous soils also have a similar power. 

 Recent researches of Thenard show that 

 phosphates are rendered insoluble when 

 they come into contact witn alundna or 

 oxide of iron, and that these are de- 

 composable again by soluble silicates, and 

 in that way the phosphates rendered 

 available. Now, supposing the phosphates 

 are taken up in solution, it would appear 

 to be requisite in a soil containing abun- 

 dance of alumina that soluble silicates 

 should be also present. But, as I liave 

 said, Liebig thinks the roots may be able 

 to decompose and abstract parts of these 

 insoluble compounds. There may be 

 some truth in this ; and if so, we must at- 

 tribute it to certain peculiarities in the 

 constitution, as we may say, of the roots 

 themselves. As an illustration of the pos- 

 sibility of some such process, I may direct 

 attention to what takes place in ihe fungi, 

 v/here we decidedl}^ have a direct action 

 of the surface of roots upon the media in 

 which they grow. We know that the pro- 

 cess of fermentation takes place during 

 the action of yeast on liquids with which 

 it is in contact : that is, the action of the 

 surface of the membrane of the j^east and 

 the interchange of the contents of the 

 cells with the liquid that j)roduces the 

 conversion of the wort into the alcoholic 

 tluid. It is the same with the plants that 

 produce vinegar and that cause acid fer- 

 mentation of vegetable preserves. There 

 may be an action of this kind in the roots. 

 The actual contact of the roots with the 

 substances in the soil may be requisite, 

 and in this way roots may be able to ab- 

 stract from the soil food not previously in 

 solution, but in a state of fine subdivision, 

 chemical action being rendered probable 

 by the moisture present in the root. 



