146 



THE GARDENER'S ASSISTANT. 



monium salts, 1 lb. of nitrogen in manure gave 

 an increased production of 28 - 8 lbs. of carbo- 

 hydrates in the grain and straw of Wheat, and 

 of 46-3 lbs. in those of Barley; when 86 lbs. 

 were applied as ammonium salts, 1 lb. gave an 

 increase of 29 °7 lbs. carbohydrates in Wheat, 

 37*1 lbs. in Sugar-beet, 27*6 lbs. in Mangel- 

 wurzel, and 17°5 lbs. in Potatoes. Again, when 

 86 lbs. were applied as sodium nitrate, 1 lb. 

 gave an increase of 36 '5 lbs. carbohydrates in 

 Wheat, 47 °1 lbs. in Sugar-beet, 32*2 lbs. in 

 Mangel-wurzel, 16*5 lbs. in Potatoes, and only 

 5 # 5 lbs. in the Leguminous crop — Beans. 



Thus, then, we have the apparently ano- 

 malous result, that the crops which are char- 

 acterized by yielding a comparatively small 

 amount of nitrogen over a given area, by con- 

 taining a comparatively low percentage of nitro- 

 gen in their dry substance, and by yielding 

 comparatively large amounts of the non-nitro- 

 genous products — starch, sugar, and cellulose — 

 are especially benefited by the application of 

 nitrogenous manures, and under their influence 

 yield greatly increased amounts of those non- 

 nitrogenous bodies; whilst the Leguminous crops, 

 which contain a much higher percentage of 

 nitrogen, and yield much more nitrogen over 

 a given area of land under the same soil and 

 season conditions, are much less benefited by 

 such manures. 



Without attempting to give an adequate 

 physiological explanation of this curious result, 

 some of the facts bearing upon it are briefly 

 stated by Lawes and Gilbert as follows : — The 

 non - Leguminous crops having comparatively 

 limited power of accumulating nitrogen under 

 given soil conditions, they generally require 

 nitrogenous manuring; the amount of nitrogen 

 assimilated to a great extent rules the amount 

 of chlorophyll formed; chlorophyll formation is 

 an essential condition of carbon assimilation; 

 the amount of carbon assimilated is the chief 

 measure of the quantity of produce; and since 

 the more special or characteristic products of 

 the non-Leguminous crops are the non-nitro- 

 genous substances, the carbohydrates, the na- 

 tural result of the increased assimilation of 

 nitrogen, and the consequent increased luxuri- 

 ance in plants is an increased formation of the 

 bodies which are their essential products. 



The fact is, that whilst it can hardly be said 

 that there remains an unsolved problem in the 

 matter of the sources of the nitrogen of Wheat, 

 of Barley, and of Grasses, as representatives of 

 the great family of the Graminece; of Turnips, 

 representing the Cruciferce; of some varieties of 



Beet, representing the Chenopodiacece ; and of 

 Potatoes of the Solanece — it must be admitted 

 to be quite otherwise so far as our Leguminous 

 crops are concerned. 



Do Plants Assimilate Free Nitrogen? — It is 

 nearly a century ago since the question whether 

 plants took up, or evolved, free nitrogen, became 

 a matter of experiment and discussion; and it 

 is just about half a century since Boussingault 

 commenced experiments to determine whether 

 plants assimilate free nitrogen. From his re- 

 sults he concluded that they did not; and those 

 obtained at Rothamsted by Lawes and Gilbert, 

 about thirty years ago, confirmed the conclu- 

 sions of Boussingault. In fact, it was concluded 

 that under the conditions of those experiments, 

 which were those of sterilization and inclosure, 

 in which therefore the action both of electricity 

 and of microbes was excluded, the results were 

 conclusive against the supposition that, under 

 such conditions, the higher chlorophyllous plants 

 can directly fix free nitrogen, either by their 

 leaves or otherwise. 



It may, indeed, be concluded that, at any 

 rate in the case of Gramineous, Cruciferous, 

 Chenopodiaceous, and Solaneous crops, free 

 nitrogen is not the source. Nevertheless it has 

 long been admitted that existing evidence was 

 insufficient to explain the source of the whole 

 of the nitrogen of the Leguminosm; that there 

 was, in fact, a missing link. 



According to some even recent experimenters, 

 I however, gain of nitrogen is not limited to our 

 Leguminous crops; and the modes of explana- 

 tion of the gains which have been observed are 

 1 extremely various. Thus, it has been assumed 

 that combined nitrogen was absorbed from the 

 air either by the soil or by the plant; that 

 there is fixation of free nitrogen within the soil 

 by the agency of porous and alkaline bodies; 

 that there is fixation by the plant itself; that 

 there is fixation within the soil by the agency 

 of electricity; and, finally, that there is fixation 

 under the influence of micro-organisms within 

 the soil, both with and without the accompany- 

 ing growth of higher plants. During the last 

 few years the discussion has assumed a some- 

 what different aspect. 



The question still is, however, whether free 

 nitrogen is an important source of the nitrogen 

 of vegetation generally, but especially of the 

 Leguminosai ; but whilst few now assume that the 

 higher chlorophyllous plants directly assimilate 

 free nitrogen, it is nevertheless supposed to be 

 brought under contribution in various ways, 

 but especially by being brought into combina- 



