SHADE TREES. 127 



parkways which are planted with shrubbery and trees, and consequently 

 both the nature of the species to be planted and the arrangement of the 

 individual trees should be studied in order to have them conform with 

 the general surroundings. This point of view of the matter is important 

 and should not be lost sight of, since the {esthetic arrangement of streets 

 and avenues adds to the value of adjoining estates in general. 



Susceptibility to Insect Pests and Diseases. 

 Injurious fungi and insects are indigenous to every community, and 

 many new pests are constantly being introduced, so that it is impossible 

 to draw definite conclusions as regards immunity or susceptibility of any 

 species of shade trees or ornamental shrubbery to those organisms. 'Judg- 

 ment upon the probability of injury in any particular case must be based 

 upon individual experience. There are scarcely any shade trees, how- 

 ever, which are not regularly affected by certain insects and fungi, and 

 thej' are, moreover, subject to local and sporadic attacks. Trees which 

 are exceptionally susceptible to insects, fungi and other injurious factors 

 should be sparingly planted. 



Commercial Importance. 

 Street trees are, as a rule, not planted for any commercial considera- 

 tion, and the commercial idea should always be a secondary one. It 

 happens, however, that sometimes the nature of the growth along comitry 

 roadsides is such that thinning may advantageously be done, much 

 good timber thus being obtained by the abutter; but this thinning should 

 be done with discretion. There are also quite a few trees, such as the 

 basswood and tulip, for example, and many shrubs, that are valuable 

 as honey species, and their utilitarian value in this respect should not 

 prevent their selection for planting. In European countries fruit trees 

 are often planted along the country roadsides, where they not only serve 

 ornamental purposes, but have a distinct commercial value in the pro- 

 duction of fruit. 



Street and Roadside Trees. 

 American Elm {Ubmis americana). — This is one of the most widely 

 planted trees in New England, where it reaches its height of perfection. 

 It is generally symmetrical in outline, attaining a good age, one hundred 

 to three hundred years, and often large dimensions. The best developed 

 types are majestic and more beautiful than any other tree known. Accord- 

 ing to Olmsted Brothers, landscape gardeners, "there is no other sort of 

 tree wliich gives the effect of a lofty, over-arcliing canopy of foliage, which 

 observation of village greens leads us to believe is the effect mostly to be 

 desired." It is difficult for an elm to thrive on dry, gravelly soil, and 

 when located in such situations it is inclined to be lanky, develops slowlj^, 

 and is unhealthy in appearance. It is best suited to a fertile, more or 

 less moist soil where fine sand and silts predominate, and is well adapted 



