70 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 
NOTES AND QUERIES. 
Lear-Mou.Lp. 
The leaf has been called the laboratory of the plant. It is in 
it that the great process of reduction goes on by which wood is 
made, and it is there that a host of other vegetable matters are 
elaborated under the action of sunlight. The raw material for 
this manufacture is chiefly carbonic acid, got from the air, and 
water brought up to the leaf from the soil; but the process of wood- 
making could not advance one step if this water did not contain, 
dissolved in it, inorganic substances which had been dissolved out 
of the soil by the root, or found by it already in a state of solution. 
The destination of these inorganic substances is, in the first place, 
the leaf, where they take part in the formation of complex organic 
matters which are required for the flower and fruit, and in the 
latter they are for the most part stored up to serve as nourish- 
ment for its young—the embryos wrapped up in the seed. 
Although the final destination of these inorganic matters is not 
the leaf itself, yet a very considerable proportion is unavoidably 
retained there, having been unable to find its way back into the 
stem or into the root, where the surplus store of material is usually 
preserved for future use. Thus it happens that when the dead 
leaves fall in autumn, they convey to the earth a very notable 
amount of the materials which plants require as food. These, in 
the living leaf, are in the form of organic salts chiefly; but as the 
organic matter of the leaf decays, they are left in the form of 
inorganic salts, viz., phosphates, sulphates, carbonates, etc., of 
potash, soda, lime, magnesia, and other bases, These are some- 
times described as the mineral constituents of the leaf, and some- 
times the ash constituents, for they are found in the ash when 
the leaf is burned. A very important constituent of leaf-mould 
that is not found in the ash is the nitrogenous matter. It exists 
in the leaf as albuminoid matter, but during the process of con- 
version into leaf-mould, it is more or less completely converted 
into ammonium salts and into nitrates. The process of conversion 
into leaf-mould is a slow and complicated one, and the products 
