246 



On the Applicaiim of Manures. 



Thus in both cases, variable as the proportions of the different 

 bases were^ the amount of oxygen present in them collectively 

 was as nearly as possible the same. 



And what renders the last result more remarkable is, that in 

 the fir-wood from Norway the amount of soluble salts was fifty, 

 in that from France only twenty-five per cent. The bases in the 

 former were in combination wholly with organic acids, those in 

 the latter partly with organic and partly with mineral ones, such 

 as the sulphuric, phosphoric, and muriatic. Yet even here, as 

 we have seen, the amount of oxygen present in the bases collec- 

 tively, and in consequence their saturating power, corresponded 

 almost precisely. 



Why then, it may be asked, cannot a new earth, like strontian, 

 take the place in a plant of those which form a part of its ordi- 

 nary constitution ? 



It is possible that the difference of crystalline form which ex- 

 ists between the substances under consideration may render the 

 substitution of one for the other in the structure of the living 

 plant impossible. Lime, it is to be remarked, is isornorphous 

 with magnesia, and even in some cases replaces potass and soda. 

 We can therefore understand how it happens that one of these 

 bases may be substituted for the others in plants, as well as in 

 minerals ; but between them and strontian no isomorphism 

 exists, and hence there may be some mechanical reason why this 

 substance is unsuitable to the vegetable organisation/* and there- 

 fore cannot replace the bases in question. 



There would seem, however, to be a limit to this power of 

 substitution, even in the case of substances which enter naturally 

 into the constitution of the vegetable, and which are isomorphous 

 one with the other, — for we cannot otherwise explain why it is that 



* Von Buch has offered some ingenious remarks in a memoir on the sili- 

 cification of organic bodies, pubhshed in the " Transactions of the Berlin 

 Academy,'' which seem to illustrate this latter position. "The skeleton of 

 animals," he remarks, " would have become very different had nature had 

 another substance to work with than phosphate of lime, the axes of which 

 are unequal. Such minerals only as have unequal axes, i. e., in which there 

 is one axis of greatest contraction, can become fibrous or extend themselves 

 in rays. They are those minerals in which the axis of the ray is always at 

 the same time the axis of the greatest contraction. This axis even decides 

 the predominant direction of the shooting out of the rays. It is only in 

 such minerals that these rays can so arrange themselves together as to form 

 a thin covering." 



" Were the secreted substance one having equal axes, like fluor-spar, for 

 instance, the organic life would have had thus great difficulty in arranging 

 the particles of tluor-spar when formed. Instead of rays and plates, masses 

 would have been produced; and the skeleton, and with it the entire animal 

 and its capabilities, would have been completely different from what they 

 actually are" 



