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 is tJic 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, practicahy 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 law^n 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 ofT every year, and thus 

 food materials and soil protection are removed and milch 

 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 dithculties 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 shav- 



