SOILS. 



273 



not of course be taken up by them ; and as the 

 plants constituting our cultivated crops with- 

 draw those ingredients in a varied amount, it 

 follows that unless the soils we cultivate contain 

 them in ample amount and variety, it will be 

 impossible for the plants placed above them to 

 arrive at a perfect state of development of all 

 their parts ; for, chemically speaking, and rar 

 tionally speaking too, soils cannot be expected 

 to produce crops abundantly, unless they con- 

 tain a sufficient supply of every ingredient which 

 all the crops we wish to raise require from them. 

 " The practical purpose of all analyses of 

 plants and soils should, therefore, be to make 

 us acquainted with the constituents of every 

 variety of cultivated crop at their different stages 

 of growth, and to ascertain whether or not each 

 soil in use contains a sufficient supply of such 

 ingredients. The analysis of plants should have 

 thus a twofold object — namely, to guide the 

 cultivator in the treatment of the plants at the 

 various stages of their growth, and to instinict 

 him as to what quantity the ripe plant in its 

 healthy state finally carries off of those ingre- 

 dients from the soil." 



Professor Johnston, in " Lectures on Agri- 

 cultural Chemistry and Geology," observes, 

 " The latter only of these two apphcations of 

 such knowledge has hitherto been kept in view 

 by chemists ; and so little has been done in re- 

 ference to it, that we scarcely know as yet what 

 any one eviire plant, when fully ripe, carries off 

 from the soil. In reference to the former appli- 

 cation, the few imperfect researches detailed in 

 the preceding sections (of the second edition of 

 his Lectures) contain all that we yet know. We 

 may well say, therefore," he concludes, " that 

 our knowledge of the inorganic constituents of 

 plants is yet in its infancy, and that our present 

 opinions upon the subject ought, therefore, to 

 be permitted to hang very loosely about us." 



The following table, showing the per-oentage 

 of mineral ingredients taken from the cultivated 

 soil by some plants, is given by Mr Stephens : — 



On the results given in the above table, to- 

 gether with three others of a similar nature by 

 Mr Stephens, Professor Johnston makes the 

 following observations : " The quantity of 

 inorganic matter contained in the same weight 

 of the different crops we raise, or of the different 

 kinds of vegetable food we eat, or with which 

 our cattle are fed, is very unlike; and the quan- 



tity contained in different parts of the same 

 plant is equally unlike. These results cannot 

 be the effect of accident. They are constant 

 on every soil, and in every climate ; they must, 

 therefore, have their origin in some natural 

 law. Plants of different species must draw 

 from the soil that proportion of inorganic 

 matter which is adapted to the constitution, 

 and is fitted to supply the wants of each ; while 

 of that which has been admitted by the roots 

 into the general circulation of the plant, so 

 much must proceed to and be appropriated by 

 each part as is suited to the functions it is 

 destined to discharge. And as from the same 

 soil different plants select different quantities 

 of saline and earthy matter, so from the same 

 common sap do the bark, the leaf, the wood, 

 and the seed select and retain that proportion 

 which the healthy growth and development of 

 each requires. It is with the inorganic as with 

 the organic food of plants — some draw more 

 from the soil, some less ; and of that which cir- 

 culates in the sap only a small portion is 

 expended in the production of the flower, though 

 much is employed in forming the stem and 

 leaves." Of the great utility of analysis Dr 

 Ure observes, that " no system can be devised 

 for the improvement of land independently of 

 experiment; but there are few cases in which 

 the labour of analytic trials will not be amply 

 repaid by the certainty with which they denote 

 the best methods of melioration, and this will 

 particularly happen when the defects of compo- 

 sition are found in the proportions of the primi- 

 tive earths. In supplying organic matter a 

 temporary food only is provided for plants, 

 which is in all cases exhausted by means of a 

 certain number of crops; but when a soil is 

 rendered of the best possible constitution and 

 texture with regard to its earthy parts, its ferti- 

 lity may be considered as permanently estab- 

 lished. It becomes capable of attracting a very 

 large portion of vegetable nourishment from the 

 atmosphere, and of producing its crops with 

 comparatively little labour or expense." 



Determining the quality of soUs mechanicaUy 

 and empirically. — The difficulties which present 

 themselves to most cultivators in carrying out 

 a scientific chemical analysis of soils have been 

 noticed : we shall now briefly state more 

 simple means by which the most important 

 constituents of soils may be determined, so far, 

 at least, as is applicable to cultivation. 



The best practical directions on this head are 

 those published in the " Encyclopedia of Gar- 

 dening," of which the follovping is an abbreviated 

 extract : — 



" The specific gravity of a soil may be ascer- 

 tained, by introducing into a phial which will 

 contain a known quantity of water equal volumes 

 of water and of soil; and this may easily be done 

 by pouring in water till it is half full, and then 

 adding the soil till the fluid rise to the mouth. 

 The difference between the weight of the soil 

 and that of the water will give the result. Thus, 

 if the bottle contains 400 grains of water, and 

 gains 200 grains, when half filled with water 

 and half with soil, the specific gravity will be 2 

 — that is, it will be twice as heavy as water; 



