126 MASS. EXPERIMENT STATION BULLETIN 170. 



ing is to secure quick results; hence during recent years much use has 

 been made on streets of the Carolina poplar and soft maples instead 

 of the better and more slowly growing species, such as rock maples, elms 

 and oaks. Excepting a few rapidly growing trees like the poplars and 

 others, there is not much difference in the rapidity of growth of different 

 species if they are given ideal conditions. While the production of quick 

 growths is quite legitimate in planting, the idea of a permanent effect 

 should not be lost sight of; and it is possible to accomplish both of these 

 results by methods of planting. 



Shode Production. 



The amount of shade produced by any kind of tree depends on the 

 shape of the crown and the density of the foliage. The more rapidly a 

 tree grows the more quickly shade is secured. The shape of the crown 

 varies with different species, but may be readily modified in such trees 

 as the poplar by pruning. Shade constitutes the important feature in 

 street trees, and is perhaps the most essential qualification of an orna- 

 mental tree. 



Root Peculiarities or Habits. 



The nature of the root development is an important factor in the 

 selection of shade trees. Such trees as the maple and elm possess large, 

 spreading root systems which are generally interfered with by street 

 repairs, excavations, etc., while some other trees more restricted in their 

 root development more often escape injury. The tendency of the roots 

 of some trees to penetrate drainage and sewer pipes is an objectionable 

 feature, as is also the upheaval of sidewalks, dislocation of curbings, etc., 

 which result from the root development of certain species of street trees. 



Neatness. 



Much objection is often made to species like poplars, horse-chestnuts, 

 etc., that produce litter, which requires frequent cleaning up. Some 

 fruits, such as the mulberry, are mucilaginous and often become danger- 

 ous on sidewalks. Nut trees are also likely to be objectionable on resi- 

 dential streets because of the nature of their fruit and the liability of 

 injury to the trees when it is gathered. It should also be mentioned that 

 certain trees such as the staminate form of Ailanthus which emit 

 disagreeable and irritating odors are undesirable. 



^Esthetic Value. 



The modern civic requirements in street planting demand not only the 

 selection of healthy and vigorous trees and their general adaptation to the 

 physical conditions surrounding them, but the consideration of beauty, 

 taste and general arrangement as regards surroundings and conformity 

 to an intelligent treatment, or, in other words, the aesthetic and land- 

 sr-a.pt' features. At the present time city streets are often provided with 



