Soil Improvement 77 
whereby physiological diseases are prevented or cured, and 
mechanical injuries rendered harmless. Too much stress 
cannot be laid upon the need of such care. Tree owners 
do not seem to realize that, after the plantation is made, it 
still requires attention; that most trees deteriorate or die 
because they are underfed and allowed to dry up. Sufficient 
water-supply 1s the most important means of maintaining 
healthy tree growth. 
Soil Improvement. ‘The most natural conditions for tree 
growth are found in the virgin forest: a soil continuously 
shaded, practically free from grass and weeds, covered with 
a heavy mulch of decaying foliage and of humus, which 
prevents evaporation and keeps the soil granular, easily 
penetrable to water and air, and well supplied with food 
materials. 
Street trees and lawn trees are not growing under natural 
conditions. In the one case the pavement keeps much of 
the water from penetrating, while in the case of the lawn, 
the grass competes severely with the tree for water, and the 
natural mulch of foliage is raked off every year, and thus 
food materials and soil protection are removed and much 
moisture is allowed to evaporate. 
Such trees are, therefore, more or less on starvation rations; 
they show almost always that they are underfed, or else suffer 
in their respiration, and, if any other contributive cause for 
unhealthy condition is added, they readily succumb, espe- 
cially as they grow older and the difficulties of securing their 
water-supply increase with age. 
In lawns, therefore, and in streets, where practicable, 
the sod should be taken up from time to time, or the soil 
stirred so as to secure better aeration, and a dressing of 
hardwood ashes, of garden mold or of well rotted stable 
manure applied, and possibly a mulch of spent bark shay- 
