246 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 
articles appeared in the various forestry journals concerning the 
use of appropriate artificial manures, with the result that the 
question began to receive general attention. 
In the present year Dr Fr. Giersberg has brought the matter 
up to date by the issue of a third edition of his pamphlet on 
“Artificial Manuring in Forestry,” in which he shows that arti- 
ficial manures may, with the greatest advantage, be used in the 
nursery and in the forest itself; in other words, he shows that 
trees at all stages of their growth can derive the greatest benefit 
by the judicious application of appropriate food materials to the 
soil, both in the nursery and in the open. 
In order to make the matter perfectly clear, it is advisable that 
we should start by considering the question from its foundation. 
We know that the body of a tree, like the body of an animal, is 
composed of organic substances. This organic substance is 
combustible, and when burned a portion is converted into certain 
gases which escape into the air, while a certain incombustible 
portion remains behind as ash. Hence the plant-body is com- 
posed of comkustible and incombustible materials. Until about 
the middle of the nineteenth century the ash constituents were 
regarded as accidental and useless in the economy of the plant, 
but nowadays we know that this view is only partly true. The 
ash may be made up of various mineral constituents—some of 
which are no doubt useless and accidental, while ethers are 
absolutely essential Among other things, the ash always 
contains potassium, calcium, magnesium and iron, and we 
know that these elements are essential constituents of the food 
material, since, by means of appropriate culture experiments, 
it has been found that green plants will not grow healthily unless 
supplied with all of those substances. Further, by leaving out 
any one in turn from the food material offered to the plant, we 
learn the function which it is destined to perform in nutrition. 
Six of ten essential elements, viz., carbon, hydrogen, nitrogen, 
oxygen, sulphur and phosphorus form constituent parts of the 
living substance of the plant. Potassium appears to be necessary 
in the original formation of sugar and starch, as well as in the 
subsequent changes which these substances undergo in the body 
of the tree, although it does not form a constituent part of them. 
Iron is essential in the formation of the all-important green 
colouring matter of the leaves. Calcium is regarded as essential in 
the assimilation of carbon dioxide by the green leaves, and also in 
