THE FARMERS' REGISTER. 



345 



much oxygen and nitrogen mixed together, but 

 when an electric spark is passed through a quan- 

 tity of air, a certain quantity of the two unite 

 together chemically, so that every spark that 

 passes forms a small portion ol' nitric acid. A 

 flash of lightning is only a large electric spark; 

 and hence every flish that crosses the air pro- 

 duces along its path a quantity of this acid. 

 Where thunder-storms are fiequent, much nitric 

 acid must be produced in this way in the air. Ii 

 is washed down by the rains, in which it has 

 frequently been detected, and ihus reaches the 

 soil, where it produces one or other of the nitrates 

 above mentioned. 



" It has been long observed that those parts of 

 India are the most fertile in which saltpetre exists 

 in the soil in the greatest abundance. Nitrate of 

 soda, also, in this country, has been found won- 

 derfully to promote vegeta'ion in many localities; 

 and it is a matter of frequent remark, that vegeta- 

 tion seems to be refreshed and invigorated by the 

 fall of a thunder-shower. There is, therefore, 

 no reason to doubt that nitric acid is really bene- 

 ficial to the general vegetation of the g'obe. And 

 since vegetation is most luxuriant in those parts 

 of the globe where thunder or lishtning are most 

 abundant, it would appenr as if the naiural pro- 

 duction of this compound body in the air, to be 

 afterwards brought to the earth by the rains, were 

 a wise and beneficent contrivance by which th.e 

 health and vigor ol universal vegetation is in- 

 tended to be promoied. 



"It is from this nitric acid, thus nniversally 

 produced and existing, that plants appear to de- 

 rive a large, probably, taking vegeta'ion in frene- 

 ral, the largest portion of their nitroiren. In all 

 climates they also derive a portion of ihis element 

 from ammonia ; but less from this source in tropi- 

 cal than in temperate climates." 



Besides nitric acid and ammonia, there are 

 other substances to which we believe plants owe 

 a part of their nitrogen ; but these, we allow, are 

 to be considered as the most important, and we 

 shall therefore hasten forward to the consideration 

 of other topics. 



When plants have obtained carbon, in the form 

 of carbonic acid, hydrogen and oxygen in the 

 form of water, and nitrogen in that of nitric acid 

 and ammonia — how does the living plant trans- 

 form these substances, so as to convert them into 

 portions of its own substance? By what power 

 is the alteration etlecled— by what succession ol 

 chemical changes is the ifinal result brought 

 about 7 This is a most interesting part of ihe 

 subject, which our limits prevent us from attempt- 

 ing to enter upon. We may merely state, thai 

 the author shows, in a rigorously exact manner, 

 how, in the interior of the plant, the starch of the 

 seed is first converted into the sugar of the sap, 

 how this is then converted into starch, or into 

 woody fibre, and the latter again, when it is re- 

 quired, brought back into the s'ate of starch or 

 Bugar. He shows also, how nearly all these 

 changes can be imitated by the art of the chemist 

 in his laboratory ; and hence infers that what 

 takes place in the interior of the plant, is no way 

 mysterious in kind— it ie mainly a series ol purely 

 chemical changes. But the mystery in living 

 vegetables, as in living animals, is the process 

 by which all these changes are regulated — which 

 saye, here such a change must take place, and to 

 Vol. X.-44 



such an extent. A living plant is a cunningly 

 contrived machine, of which chemistry can de- 

 scribe the wheels and the movements, but of which 

 she may never be able to discover, certainly she 

 can never hope to supply, the moving power. 



The second part of the Lectures is devoted to 

 the inorganic constituents of plants, and to the 

 geological and chemical relations of soils. We 

 shall first complete our survey ol'the newest views 

 in regard to the food of plants. We have already 

 adverted to the fact that the various parts of ve- 

 getables, when burned in the air, leave behind 

 a comparatively inconsiderable proportion of 

 earthy or incombustible matter. Such is the 

 common woodash, and such the ash left when 

 heaps of weeds or the parings of our grass fields 

 are burned. What is the use of this incombusti- 

 ble matter — what purpose does it serve in the 

 plant — whence is it derived 1 Is it only present 

 by accident — or does the healthy plant always 

 con'ain it? Is its quantity constant, and does 

 the same plant always yield the same kind of 

 ash? For an answer to all these questions we 

 must refer the reader to the works before us; 

 but it will be interesting to trace ihe progress of 

 opinion upon this branch of vegetable chemistry — 

 not only because the eubjrct is exceedingly 

 curious in itself, but because the present state of 

 opinion on this subject is connected with all the 

 recent improvemems in agricultural practice, has 

 suggested many of them, and is now directing 

 the enlightened farmer, often unconsciously, in 

 all his most promising practical investigations. 



The ash of plants, until a very recent period, 

 was considered by the vegetable physiologists — 

 who, indeed, esteemed themselves the judgei 

 paramount in this domain — as accidentally pre- 

 sent, or at least as performing no important or 

 necessary function in reference to vegetable life. 

 No account was taken of it, therefore, in theory: 

 and in practice — little as some may think agri- 

 cultural practice in past times to have been affected 

 by theory — in practice this opinion of the phy- 

 siologists led to Ihe adoption and justification of 

 the most pernicious system of husbandry; for 

 they naturally reasoned thus: If the organic or 

 comltusiible part of plants be the only important, 

 vital or essential portion, then, of manures such 

 as are prepared in the farm-yard, it is also the 

 only essential part — and in soils the vegetable or 

 animal matier — the combustible parts of them, 

 that is, which alone supply the plant with or- 

 ganic food — must likewise be the only essential 

 portion. Accordingly, vegetable manures, or 

 animal excrements, directlj^ derived from vegeta- 

 bles, were alone considered necessary to fertilize 

 the land and to fi>.ed the crop; and the vegetable 

 maticr in the soil was esteemed to be at once 

 the source and the index of its agriculturni capa- 

 tiiliiies. So firmly rooted was the opinion, and 

 so widely spread, and eo long has it lingered 

 among practical men, that some of our readers 

 may, even while they peruse these sentences, 

 be unwilling to acknowledge, or have had no 

 opportunity of being satisfied, that it is en'irely 

 erroneous. However, among other errors in 

 practice, it led to the total neglect of the inorganic 

 or incombustible part of the crops carried fi-om the 

 land. It was supposed that if a sufficient qitantity 

 of vegetable matter was always kept in the soil. 



