EXPERIMENT STATION WORK, LI. 13 



early stages the tree may be rejuvenated by digging out a quantity of the poor 

 soil and replacing with good loam; if the specimen shows too great a degree 

 of weakness it had better be substitued by a younger, vigorous specimen. 



Along city streets, where conditions are so often unfavorable to 

 tree growth, the holes for newly planted trees should be filled with 

 loamy soil, and they should be large enough to provide for future 

 root development. A bed 4 feet wide by 8 feet long and 2 feet deep is 

 none too large. In streets which are often congested with people it 

 may not be feasible to leave such a large open space for each tree. In 

 such cases an iron grating, as shown in figure 5, can be placed over 

 the area that is not paved. This will prevent the soil from becoming 

 impenetrable to surface water. 



In large manufacturing centers smoke and atmospheric gases are 

 often present in sufficient quantities to seriously injure or even kill the 

 surrounding trees. " The functions of the leaves are retarded in two 

 ways : First, the breathing pores, or stomata, become choked with the 

 soot; and, second, many gases in themselves may be poisonous, even 

 when diluted with the atmosphere." Since most trees are subject to 

 the effects of smoke and 

 gas, it is highly advisable 

 that "trees should be se- 

 lected on the basis of re- 

 sults secured with similar 

 species in other cities and 

 towns under similar con- 

 ditions." Municipal au- FIG. e.-A grating to cover " well" 

 thorities may be able to 



prevent the excessive production of smoke and gases, but it is very 

 probable that they will always be present in considerable quantities 

 wherever factory interests are large. 



Overcrowding of street trees can be prevented if the trees are prop- 

 erly spaced when planted. Information relative to the space required 

 for the normal development of our shade-tree species is not difficult 

 to obtain. In situations where there are no shade trees, there is a 

 tendency to plant close, in order to secure shade quickly. There is 

 danger in the close planting of young trees, however, due to " the 

 necessity of their removal at a subsequent date, when only a person 

 possessing the courage of his convictions will take out the trees that 

 should be sacrificed. * Every town and city possesses trees 



that are suffering from this evil of overcrowding. Each community 

 should designate some intelligent person to direct the work of caring 

 for the pruning of such trees, who, despite false sentiment, will 

 accomplish the work." 



Trees that have been seriously girdled through failure to remove 

 the label wires, or from other causes, can often be saved by bridge- 



360 



