122 INTRODUCTION TO BOTANY 
means of roads helps to keep small fires from spreading, but 
in warm dry weather a coniferous-forest fire under full head- 
way makes such leaps that it is seldom stopped until it reaches 
extensive clearings or rivers or other large bodies of water. 
Fic. 99. Oak trees growing in the open 
White oak at the left and red oak at the right 
5. Parasitic fungi and the saprophytic kinds which cause the 
decay of fallen trunks and branches or felled trees (figs. 182 
and 199) should be burned, when this is not too expensive and 
when it can be managed without danger of starting forest fires. 
