23 
insect standpoint may be seen at a glance the same trees have been 
rearranged in a separate table as follows: 



Variety of tree. ee . Variety of tree. sane 
Gingko (Gingko biloba) ......----------- 3.0 || Shingle oak (Quercus imbricaria) .-.--- 2.0 
Tulip tree (Liriodendron tulipifera) ..-. 3.0 | Slippery elm (Ulmus pubescens) .-.----- 2.0 
Sugar maple (Acer Saccharum) ....----- 2.5 | Norway maple (Acer platanoides)...-... 2.0 
1Red oak (Quercus rubra) .....--------- 2.5 || Hardy catalpa (Catalpa speciosa) ...--- 2.0 
Tree of heaven (Ailanthus glandulosa) - . 2.5 || European linden (Tilia vulgaris) ..-...- 155 
1 Scarlet oak (Quercus coccinea) ..-.----- 2.5 | American elm (Ulmus americana). .--.. aD 
Yellow oak (Quercus velutina) ...-..-.--- 2.5 || Hackberry (Celtis occidentalis) ......--. 1.5 
Willow oak (Quercus phellos) ..----.-.--- 2.5 | Silver-leafed maple (Acer saccharinum) 155 
Black maple (Acer nigrum) ...---------- 2.5 || Oriental plane tree (Platanus orientalis) 1.5 
Japanese sophora (Sophora japonica)... 2.5 | American plane tree (Platanus occi- 
Horse-chestnut (Asculus hippocasta- GENCHAS) Hoan ac merece oer esiass a aeine ne 
WED) acti cate aotecapnedosoek Beceepese 2.0 | American linden (Tilia americana) ---. 5 
Red maple (Acer rubrum) ...----------- 2.0 | Honey locust (Gleditschia triacanthos) - 1.0 
Small-leafed linden (Tilia microphylla) - 2.0 || Scotch elm (Ulmus montana) .......--- 1.0 
White oak (Quercus alba) ...---.------- 2.0 || Cottonwood (Populus monilifera)..---- ait 
Sweet gum (Liyuidambar styraciflua) . - 2.0 || Balm of Gilead (Populus balsamifera v. 
Bur oak (Quercus macrocarpa).....-.--- 2.0 CONOACANS) ws aiinivra nae Soe eias wats oe = 5 
Kentucky coffee tree (Gymnocladus European elm (Ulmus campestris) .--.. -5 
ULDUSUS) seme c Sees eins we ncease eek ass | 2.0 || Black locust (Robinia pseudacacia) ..-. 5 
Sycamore maple (Acer pseudo-platonus) . 2.0 || Box elder (Negundo negundo) .......--. .0 




‘This estimate of the red oak and scarlet oak was based largely on the beautiful 
condition of certain trees growing in the streets of Washington, D. C. Since the 
publication of the Yearbook article, however, several of these trees have deyeloped 
rather serious cases of insect injury. The locust borer (Xyleutes robiniw) has attacked 
a number of the trees, and although it is not apparently weakening their vitality to 
any serious extent, still it bids fair to do considerable damage. The trees have been 
treated by injecting a small quantity of bisulphide of carbon into the burrows and 
covering the opening with putty. In a few cases the obscure scale (Aspidiotus 
obscurus) has attacked these trees. It has not as yet killed any branches, but it 
multiplies as abundantly as its dangerous relative, 4. tenebricosus, of the maple, and 
Isee no reason why it should not be an equally injurious species. This experience 
somewhat shakes the confidence of the writer in his estimate of the rating of these 
oaks, but not to any very serious extent. 
It will be noticed that the trees listed by Mr. Fernow which we find 
to be most immune are the gingko and the tulip tree. Outside of the 
grounds of the Department of Agriculture at Washington and Cen- 
tral Park, New York, few gingko trees are grown in this country, 
except as occasional isolated examples. The tree itself is a very 
beautiful one, and singularly free from insect attack. In the long 
double row of these trees, now nearly twenty-five years old, on the 
grounds of the Department of Agriculture, but one species of injuri- 
ous insect has ever been found, and the work of this species is very 
insignificant. It is the little sulphur-yellow leaf-roller, Tortrix sul- 
phureana, 
The tulip tree, which is given the same rating, is, for practical pur- 
poses, almost as exempt as the gingko, Of late years in the District 
