CHEMICAL MANURES. 



the same order, the leaves of an evergreen hold fewer minerals than 

 do those of a deciduous tree, being renewed at a season least favor- 

 able to evaporation. 



The following figures show the proportions : 



Dried Vegetable Matter, 

 Containing 100 parts Mineral. 



Grasses 7.84 



Trees 0.94 



Wood 0.55 



Sap-wood 2.65 



Bark 7.47 



Leaves 14.20 



Deciduous leaves 6.60 



Evergreen " 2.00 



Pea-shells 5.50 



Peas 3.10 



If we make as exact a study of each mineral element as we now 

 do of the whole, we will arrive at an analogous conclusion, to find 

 that by a species of election each of these elements centres by prefer- 

 ence in a certain set of organs. Thus we find more silica, lime, 

 oxide of iron, sulphates and chlorides in the stem and leaves than in 

 the fruit and seed, where, on the contrary, sulphuric acid, potash and 

 magnesia become the predominant elements. 



Take wheat for example. In the ashes of the seed there is 46 

 per cent, of phosphoric acid, in the chaff, 2.54, in the straw, 2.26, and 

 only 1.70 in the roots. 



What I have just said of phosphoric acid is equally true of mag- 

 nesia and potash, the proportions of which change from one organ to 

 another, as will be seen by the following table : 



IN 100 PARTS OF ASHES OP 



Roots. Straw. Seed. . . 



Phosphoric acid 1.70 2.20 46.00 



Magnesia: ,.... 1.97 3.92 13.77 



Potash 2.87 15.18 32.59 V 



Lime 0.88 3.00 1.19 , 



The differences here found in wheat exist in all plants without 

 exception. 



Thus, the distribution of minerals is not left to chance, but is sub- 

 ject to fixed laws ; all aid in the general structure of the plant, but 

 each centres in a fixed organ or system of organs. We will now find 

 the cause of f this unequal distribution. 



In the economy of living beings all the functions, varied as they 

 are, tend to one end viz., the reproduction of the species for all 

 time. They are ordered with a view to this important result. But 

 to gain this object, the embryo contained in the seed must have 

 within its reach all those minerals necessary to the first acts of 

 vegetable life. Hence, the seed is so abundantly supplied with 

 phosphoric acid, potash and magnesia. It is a kind of reserve laid 

 by for the first movements of the embryo. , 



