10 CHKM1CAL MANURES. 



If you carefully read the preceding table, you will be struck by 

 the contrast between the potash and phosphoric acid. 



Phosphoric acid is pretty uniformly distributed through all the 

 organs, the seed excepted. Not so with potash. The concentration 

 of phosphoric acid in the seed is sudden ; the proportions of potash 

 increase by degrees, and, you will observe, in proportion as the organ 

 nears the seed. Why this sudden increase on the one side and 

 gradual progress on the other ? 



An old remark of Theodore de Saussure informs us : 



The phosphates of lime and magnesia are insoluble in water ; but 

 there is a double phosphate of potash and lime, and a double phos- 

 phate of potash and magnesia, both of which are soluble in water. 



Potash or, to speak more exactly, alkaline phosphates favors, if 

 it does not determine, the change of terraqueous phosphates into 

 tissues. Now, at the time the seed forms vegetation is retarded and 

 the organs begin to dry. It is evident, then, that the superabundance 

 of alkaline salts must favor the passage of terraqueous phosphates ; 

 therefore, the nearer the seed the greater the quantity of potash, and 

 consequent increase of terraqueous phosphates. 



Let us look, now, to the distribution of the organic elements. 

 Here a fact strikes us. These elements, four in number, represent at 

 least ninety -five per cent, of vegetable matter. Here let me say that 

 although the minerals do not figure largely, we may not from that 

 conclude they are less important than the organic elements. Want- 

 ing them, vegetation would be impossible ; it would be languishing 

 and uncertain if the soil were not sufficiently supplied with them. 

 In their distribution through vegetation the organic elements present 

 another contrast to the mineral elements ; three of them carbon, 

 hydrogen and oxygen are exhibited in almost unvarying propor- 

 tions. All plants and all organs, without distinction, contain the 

 same quantities of these. Trees, shrubs, simple plants, roots, stems, 

 barks, branches, leaves, fruits and seeds maintain an invariable 

 balance in proportions of carbon, hydrogen and oxygen. 



With azote it is different. We may say of that what has already 

 been said of phosphoric acid potash fruits and seeds contain more 

 of it than the other organs, because during germination the embryo 

 lives on the seed, and within its small circumference it must find 

 azote as well as minerals. 



In vegetable matter carbon and oxygen are exhibited, each at 40 

 to 45 per cent., hydrogen from 5 to 6 per cent., and azote from 1 to 

 2 per cent. 



I have promised to define vegetable composition with exactness and 

 clearness. It seems to me that the preceding data do so. 



But it is not enough to know what composes vegetable matter ; we 

 must also know how it is 'formed, and how those elements combine 

 which shape and increase its organs. 



Here the process differs at all points from that proper to minerals. 

 If a solution of marine salt is exposed to the sun, as the liquid 

 evaporates crystals are deposited too fine to be seen but with a mag- 

 nifying glass. Soon, however, their forms become visible, and we 



