THE FARMER'S MAGAZINE. 



11 



more nitrogen than was originally present in the aecda. They 

 were freely exposed to the atmosphere, but they were in- 

 capable of extracting from the atmosphere sufficient nitrogen 

 to do much more than to keep them alive. The plants, how. 

 ever, in the brick-duat 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 a^ 

 healthy 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 pro- 

 duced, taking the seed as one, a dry product of little more than 

 three parts ; while the one with nitrate of potash and phos- 

 phate of lime produced 198 parts; and that of the phosphate 

 of lime and carbonate of potash about four parts. The plant 

 in the nitrate of potash showed 200 times the quantity o^ 

 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 substance 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 

 amounted to 120 grains, or eighty times the former. The car- 

 bonic acid, which was decomposed in twenty-four hours by the 

 starved plant, was only 2^ cubic centimetres ; while that fed 

 upon nitrate of potash consumed in the same time 182 ; show- 

 ing that the presence of nitrogen in the manure was that sub- 

 stance which not only produced the development, but produced 

 the increased quantity of nitrogen in the product and the fixa- 

 tion of the carbon. These experiments, physical and chemical, 

 bring the evidence from one side of the question to complete 

 the reasoning furnished by the anatomical conclusions to which 

 I previously alluded. The results are remarkable in the two 

 cases. Boussingault's experiments show that nitrogen is the 

 efficient agent in the assimilation of food, and the anatomical 

 examination of the tissues demonstrates the actual process of 

 elaboration taking place in the midst of these nitrogenous sub- 

 stances. 



There are one or two other points to which 1 must briefly 

 advert, as of interest in reference to this matter. I may men- 

 tion, in the first place, that we have lately had a new hypo- 

 thesis 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 absorption 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 

 Tbenard show that phosphates are rendered insoluble when 

 they come into contact with alumina or oxide of iron, and that 

 these are decomposable 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 re- 

 quisite in a soil containing abundance of alumina that soluble 

 silicates should be also present. But, as I have 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 attribute it to certain peculiarities in 

 the constitution, as we may say, of the roots themselves. As 

 an illustration of the possibility of some such process, I may 

 direct attention to what takes place in the fungi, where we de- 

 cidedly have a direct action of the surface of roots upon the 

 media in which they grow. We know that the process of fef 

 meatation 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 yeast and the interchange of the con- 

 tents of the cells with the liquid that produces the conversion 

 of the wort into the alcoholic fluid. It is the same with the 

 plants that produce vinegar and that cause acid fermentation 

 of vegetable preserves. There may be an action of this kind 

 in the roots. The actual cor\tact of the roots with the sub- 

 stances in the soil may be requisite, and in this way rr.ots 

 may be able to abstract 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. 



It would have been desirable perhaps to have directed 

 your attention to some speculations with regard to the in- 

 fluence of phosphate of lime upon roots, but time will not 

 admit of this, and moreover our knowledge on the subject 

 is extremely limited. No doubt there is a kind of specific 

 action of phosphate of lime upon roots, that it does favour 

 the production of roots at particular seasons, and under 

 particular conditions of cultivation. How and why it does 

 so science, I think, is unable at present positively to 

 demonstrate, and it is too late to-day to enter into any 

 speculations with regard to this point. I may say, however, 

 that for the settlement of that point only carefully devised 

 and extensive experiments can be of any service. In regard 

 to such experiments, I will make one remark in con- 

 clusion of my lectiu'e. I must differ, or apparently differ, 

 to a certain extent, from our professor of chemistry in one 

 opinion to which he gave expression in his late interesting 

 lecture concerning the ofHce of science in relation to prac- 

 tice. I am not of a sanguine disposition— am considered 

 rather cautious than otherwise ; but I must declare that I 

 look upon science as not only the means of explaining what 

 has been done, but as the great instrument by which we 

 shall discover means of doing what we have never done 

 before. It is quite true that in the present state of know- 

 ledge agricultural practice may be in advance of science : 

 theory has not worked its way up to the point 

 in which it can explain all science, much more 

 lay down any new rules for guidance. That is the 

 result of the condition of the particular branch of 

 science : it is not the fault of the science itself. That it is 

 unable to do so, arises from the condition in which the 

 science is placed by the natural course of events. Physio- 

 logy depends for one complete set of its data upon organic 

 chemistry ; organic chemistry could never be properly 

 worked out until mineral chemistry had made considerable 

 advances; and even were these departments of inquiry per- 

 fect, there is still meteorology in its infancy, incapable as 

 yet of explaining peculiarities of climate, so as to unable 

 us in some degree to foretell events with regard to weather, 

 as the astronomer does as regards the movements of the 

 heavenly bodies. I do not consider that this imperfect state 

 of our information demands the conclusion that we are to 

 give up the position of science as the leader of practice. I 

 think that when we look upon the other branches of science 

 which have to deal with simpler forces and less complicated 

 questions, we have every reason to suppose that with 

 proper prosecution of experimental inquiry in physiology, 

 we may be able to use speculation as a means of greatly 

 improving and advancing our practical knowledge. When 

 we see the results of speculation in physics and chemistrj', 

 in the conquests of the powers of steam, electricity, light — 

 all products of speculative or abstract science — I think we 

 should not doubt that when physiology has ascended to the 

 same relative stage, that branch of science will take its 



