STREET AND HIGHWAY IM.AX'II X(i. 77 



adapted to the lines of an arbor, of real architectural merit and well 

 planted." This is a tentative idea calling for much more thought 

 before acceptance or rejectance. 



The general requirements of trees are that the soil should be of 

 reasonably fine texture, so that the water does not drain away too 

 readily or stand too long so that baking is the result afterwards. 

 Where the soil does not answer these requirements it is highly profitable 

 to make some effort to improve it. In those towns where there is an 

 adequate street-cleaning department, the sweepings, provided they do 

 not contain too much rubbish, are often useful in adding humus to the 

 soil. Where all the earth must be supplied, the best possible should, of 

 course, be obtained. 



The old saying that the spread of the roots is proportionate with 

 the spread of the tops, often leads one to wonder how street trees can 

 survive. For them the soil should be at least three feet deep and should 

 be in good condition for as large a radial distance from the trunk as 

 possible. With these conditions the trees can usually adapt themselves 

 to their other limitations. 



One point which is sometimes overlooked, is that soil which was 

 below the original grade and is now surface soil may or may not be fit 

 soil for planting. In very deep soils it does not make much difference, 

 but usually the first three feet of soil are of better quality than the 

 subsoil. A fill, on the other hand, often gives good soil for planting, 

 depending, of course, upon the original source of the dirt. One danger 

 might possibly arise, and that is, that the fill might be of more porous 

 soil than the original grade, with the result that the water might stag- 

 nate along the old grade level. All these points must be cared for. 



On most streets we find provision for planting made in strips of 

 parking of varying widths along the outer edges of the pavement. 

 These are broken only for driveways and entrance paths. The matter 

 of width is one worthy of considerable attention. As we find them 

 to-day they vary from eighteen inches up. Obviously it is absurd to 

 plant a tree in an eighteen-inch parking, but it is done, and people 

 wonder why the pavements are lifted. For the best success of the 

 trees the parking space should be four feet at the very lowest, and a 

 strong preference for ten-foot parkings. For some species, particu- 

 larly palms, peppers, oaks, etc., fifteen feet is none too large. 



The roadways vary largely in width and in many cases are too wide. 

 The width must be determined, of course, by the amount and nature 

 of the traffic along the street. Hence, residential streets need not be 

 so wide as business streets. Extra width in residential districts means 

 money wasted in paving, a greater surface to develop dust and a min- 

 imizing of parking space, thus bringing the dust closer to the homes 



