IT VARIES WITH THE SPECIES OF PLANTS. 179 



In the parts of trees dried in the air there are found of inorganic 

 matter — 



In looking at the preceding tables, you cannot fail to be struck with 

 one or two points, which they place in a very clear light. 



1°. That the quantity of inorganic matter contained in the same 

 weight of the different crops we raise, or of the different kinds of vegeta- 

 ble food we eat, or with which our cattle are fed, is very unlike. Thus 

 100 lbs. of barley, or oats, or peas, contain twice as much inorganic 

 (earthy and saline matter, that is,) as an equal weight of wheat or rye — 

 and the same is the case with lucerne and white clover hays, compared 

 with the hay of rye grass. 



2°. The quantity contained in different parts of the same plant is 

 equally unlike. Thus 100 lbs. of the grain of wheat leave only ]|lbs. 

 of ash, while 100 lbs. of wheat straw leave 3^ lbs. So the dry bulb of 

 the turnip gives only 7 per cent., while the dry leaf leaves 13 per cent, 

 of ash when it is burned. The dry leaves of the parsnip also contain 

 nearly 16 per cent., though in its root, when sliced and dried in the air, 

 there are only 4^ per cent, of inorganic matter. 



In trees the same fact is observed. The wood of the elm contains 

 less than 2 per cent., while its leaves contain nearly 12 per cent. ; — the 

 wood of the oak leaves only ^ih of a per cent., while from Its leaves 4| 

 per cent, or 22 times as much are obtained. The leaves of the willow 

 and of the beech also contain about twenty times as much as the wood 

 of these trees does, when it has been dfled under the same conditions. 



These differences cannot be the result of accident. They are con- 

 stant 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 developement of each requires. It is with the inorganic, as 

 with the organic food of j)lants. Some draw more from the soil, some 

 less, and of that which circulates in the sap, only a small portion is ex- 

 pended in the production of the flower, though much is employed in 

 forming the stem and the leaves. On the subject of the present section, 

 I shall add two other observations. 



1°. From the constant presence of this inorganic matter in plants, and 

 from its being always found in nearly the same proportion in the same 

 species of plants, — a doubt can hardly remain that it is an essential pan 

 of their substance, and that they cannot live and thrive without it. But 

 that it really is so, is placed beyond a doubt, by the further experimen 



