134 MASS. EXPERIMENT STATION BULLETIN 170. 



soil and which were twenty-two years old showed an average diameter 

 of 16 inches, wliile others grown in dry, gravelly soil attained an average 

 diameter of only 12 inches during the same time. The white ash develops 

 a widespreading top, and is a fairly desirable skade tree, although in 

 too dry locations it may become affected by borers and scale insects. It 

 has suffered much in recent years from drought, winterkilling and in 

 some locations from a rust {Mcidium fraxini). Other species of ashes, 

 like the black ash, are occasionally planted accidentally for the white ash. 



Cucumber Tree or Magnolia {Magnolia acuminata) has been highly 

 recommended by some authorities for roadside planting. It has been 

 employed extensively as an ornamental tree, but no attempt so far as we 

 know has been made to utiUze it as a street tree in the north. 



Sweet Gum {Liquidambar styraciflua) is a native farther south, Mas- 

 sachusetts appearing to be a little too far north for its best development. 

 At any rate we have observed no satisfactory growth of this species in 

 this section. It is subject to winterkilling and frost cracks in the north. 



Ginkgo {Ginkgo biloha), a Japanese species, is occasionally seen on 

 lawns, and forms a beautiful avenue on the agricultural grounds at Wash- 

 ington, D. C. Well-developed individual specimens of Ginkgo may be 

 observed here and there in New England, and this tree has been used to 

 some extent for street planting. It is adapted to a wide variety of soils, 

 and is remarkably free from diseases. It develops a narrow cylindrical 

 or conical crown, which adapts itself to narrow streets. This species is 

 undoubtedly better adapted to planting farther south than in New 

 England; nevertheless, it possesses many qualifications as a desirable 

 street tree, and should be utilized for this purpose in suitable locations. 



Carolina Poplar {Populus deltoides), which is now quite extensively 

 planted, is one of the most rapidly growing species, and is a valuable tree 

 for producing quick effects. The Carolina poplar is especially useful to 

 fill in between trees of slow growth but of more desirable types. Good 

 avenues of this species may be seen about Boston in the metropolitan 

 park system, where the trees have been cut back to form a compact head. 

 Tliis tree, however, is subject to various troubles, and is short lived. Two 

 other native species of poplar, i.e., P. grandidentata and P. Iremuloides, 

 are common, but have no value for planting. 



Black or Italian Poplar {Popidus nigra) . — This species has been 

 planted somewhat as a lawn and avenue tree. It grows even more rapidly 

 than the Carolina poplar, and possesses similar characteristics. It is 

 affected by a rust {Melampsora populina) which sometimes causes much 

 defoliation. 



LoMBARDY Poplar (P. nigra var. italica) has been planted sparingly 

 for more than a century in New England, and has come into wider use 

 of late. It is used somewhat on narrow avenues, although on account of 

 its ascending and close-branching habit of growth it does not furnish 

 much shade, and is, moreover, too stiff and conventional in appearance 

 for most places. The white or silver-leaved poplar (P. alba) and the 



