Needs of Fruit Trees. 209 
mand for specific kinds and proportions of soil con- 
stituents; it is really a continuous cropping of the 
same kind; there is no opportunity, as in the case 
of ordinary farm crops, to correct the tendency to 
exhaustion by a frequent change of crops, or the 
frequent growth of those which require different kinds 
and amounts of plant-food constituents. 
“In studying methods of manuring orchards, how- 
ever, it must be admitted that the general princi- 
ples of manuring which apply to fruits apply quite 
as well to farm crops; that is, the essential con- 
stituents of manures must be the same. A fruit tree 
will not make normal growth in a soil destitute of 
nitrogen. That nitrogen encourages leaf-growth is a 
recognized fact, and, since trees grow by means of 
both leaf and root, its presence is required in the 
soil in order to promote the growth and extend the 
life of the tree. It is very evident, too, that pot- 
ash is an essential constituent in the growth of 
fruits, not only because it constitutes a large pro- 
portion of the ash of the wood of the apple, pear, 
cherry, and plum, and more than 50 per cent of 
the ash of fruit, but because it forms the base of 
the well-known fruit acids; and in order to nourish 
a tree properly, as well as to insure proper ripen- 
ing, phosphoric acid is also very essential, though it is 
apparent from such investigations as have been made 
that this constituent is relatively of less importance 
than for the cereals. 
“It is also a matter of common observation that, 
in the production of stone-fruits particularly, lime 
ce) 
