TIMBER; FORESTRY 351 
above mentioned. It was introduced from Europe in 1869 
by a scientist living at Medford, near Boston, Massachu- 
setts, in the course of some experiments on silk-produc- 
ing insects. It soon escaped into his garden, but could 
easily have been exterminated if prompt measures had been 
taken to secure every patch of eggs deposited on trees 
in the vicinity. This was not done, and the insects propa- 
gated themselves, until after twenty years they began to be 
troublesome. In 1890 efforts to extirpate the moth were 
begun on a large scale, but though from 1890 to 1897 more 
than $865,000 were expended by the state in destroying the 
moth, it still remained a serious enemy to the trees over a 
region some two hundred square miles in area. By the aid 
of United States government funds the insect is now held in 
check, but no one can say when it will be-exterminated. 
(5) Sheep and cattle must not be pastured in woods in 
which they can seriously injure the value of the timber 
product. Cattle do not usually do much damage in 
forests which consist mainly of mature trees. They de- 
stroy some young broad-leaved trees by browsing, but do 
not molest young conifers. Sheep injure young seedling 
trees by browsing, and they do much more serious damage, 
particularly on hillsides and: mountains, by grazing the 
grass too closely and cutting the turf to pieces with their 
sharp hoofs, so that it is dried up by the sun and washed 
away by heavy rains. In the Rocky Mountain region and 
along the Pacific slope in this country and over great 
tracts in southern Europe, valuable forest land has been 
converted into worthless rock and gravel-covered treeless 
slopes as a result of sheep-pasturing. 
422. Tree-Planting. — In those portions of the country 
which are naturally forest-covered it is not usually worth 
