120 WOODY PLANTS OF MASSACHUSETTS. 
side of the branch a spherical gall of one-fifth to one-quarter of 
an inch in diameter. These are found single, or two or three 
together, near the extremities of the smaller branches. If cut 
open in winter, they expose a worm or chrysalis folded up 
within a bony case. 
For an account of the modes that have been devised to pre- 
vent or remedy the mischief done by so many enemics, I must 
refer to the Report of Dr. Harris, to whom I am indebted for 
almost the whole of what I have given above, and who has 
done more than all other persons in the investigation of the 
difficult subject of the habits and ravages of the insects of Massa- 
chusetts; more, indeed, by original observation, than has ever 
before been done, by any person, in any country or State what- 
ever. Care and precaution may do something; but against 
many of these insects the unassisted efforts of men can accom- 
plish very little. Most of the birds, probably all of them, the 
smaller quadrupeds, and all the reptiles come to our aid and 
wage perpetual war upon the insect tribes. ‘The woodpeckers 
and the creepers do what they can to keep the bark of trees tree ; 
the fly-catchers take care of the leaves; a single flock of wild 
pigeons will do more than an army of foresters against the large 
solitary caterpillars which infest the oalc forests. 
The bark of most species of oak contain the tannin princi- 
ple. The cups of the Velani oak are used for dyeing and for 
tanning. Both purposes are effected by the bark of our com- 
mon black or yellow bark oak. The bark of a species of oak 
which grows in Spain, Quercus suber, furnishes the invaluable 
substance, cork, which is used in the countries where it is 
produced, not only for the purposes to which we apply it, but 
also as a lining and a carpet in brick or stone habitations. 
The bark of most of our oaks is useful to the tanner, particu- 
larly that of the white oak, the chestnut oaks, and others of the 
same group. 
Yet the great value of the oak, in all countries, is for its wood. 
It is applied to a greater variety of important purposes than 
that of any other tree. With the exception of the teak tree, it 
forms the best ship timber known; and, for this purpose, the 
white oak is, perhaps, equal to the English oak, and surpassed 
