iSSf 
Figure 333. — Sign Containing Warning about Fires. 
by human means, nearly all preventable; 952 were in¬ 
cendiary ; 1288 were caused by careless campers; and 1003 
by sparks from railroad locomotives, in violation of laws 
which call for spark arresters on engines used in or near 
the forests. 
Forest rangers also keep watch of the trees to see that 
fungus does not cause the death of trees,* and to prevent the 
spread of such diseases when they are found. In localities 
where cleared spaces in the national forests are rented for 
grazing purposes, forest rangers see that the regulations 
concerning the grazing of cattle are observed, collect fees, 
THE WORK OF A FOREST RANGER 359 
more effective than any kind of device, however, and most 
.efforts are being made in that direction. Signs and posters 
warn persons to be careful. 
Campers are taught how to select a spot for a fire, how to 
care for it to prevent its being a menace, and how to put it 
out when breaking camp. 
Of the forest fires in the United States during 1917, 7814 
in number, 2132 were caused by lightning, and the others 
