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pih>ci:ki>in(;8 of iiik 



havo learnt iho naliiro of tho siibsUinces thus absorbed by any 

 plant we cannot therefore eonelude that they are essential to the 

 urowth of that particular i)lant, because we find in some cases 

 that the same plant when i^roNS n on another soil absorbs different 

 earthy substam es, which are therefore apparently able to replace 

 those, whicl> the ])revious analysis mi^ht have led us to consider 

 essential to the i^rowth of the plant. The invcstit::ation of this 

 subjec t is full of interest and importance, and will probably lead 

 to valuable results, more especially as rcij^ards the imj)rovement 

 of soils and the modes of rcndcrinii; them best iitted for the 

 cultivation of partii ular crops. 



One subject on which this encjuiry would throw li^ht is the 

 nianurinii: of trees. At present comparatively very little is known, 

 rcspectint^ the kind of manure best suited to the various kinds of 

 timber or fruit trees. It is frequently stated that manure is hurt- 

 ful to this or that kind of tree, merely because dung and similar 

 matters are found injurious. It is clear that in such cases the 

 kind of manure aj)plied was not suitable to the plant, but it is not 

 therefore to be concluded that all manure would be hurtful j it 

 might as well be argued that because an animal could not be 

 supported on a certain kind of food, that therefore no food what- 

 ever could kecj) it alive. The error has lain in attempting to apply 

 manure at random, without knowing what substances the tree 

 requires. Nothing certain is known respecting the influence 

 which inorganic matters contained in the soil have on the forma- 

 tion of woody fibre for example ; that they have considerable 

 influence there can be little doubt, from the very different quality 

 of the wood of the same tree when grown on different soils. No 

 doubt the relative goodness of timber is greatly influenced by 

 climate, dryness of air, periodical winds and other similar causes, 

 but at the same time it is certain that the nature of the soil is of 

 great importance and it is very probable that its chemical compo- 

 sition as well as its mechanical texture, produce considerable 

 variations in the strength and other properties of wood. A 

 knowledge of the inorganic substances required by plants, and 

 the object effected by their absorption, must lead to great im- 

 provements in the application of inorganic manures. 



A series of curious experiments has been made by Dr. Daubeny, 

 which appear to prove that plants, to a certain extent, have a 

 power of selp:ction in their roots. He found that when plants of 

 Barley were watered with a diluted solution of a salt of strontia, 

 none of the earth was carried up into the plant ; and he further 

 ascertained that in this case the strontia was not first absorbed 

 and subsequently returned by the rof ts, but that apparently such 

 deleterious matters were at once rejected, and not suffered to 



