176 PRACTICAL FORESTRY 
which they would consume may be more advanta- 
geously used. 
In many districts clambering vines and worthless 
briers and bushes often have complete possession of 
the soil. The various species of grape which mingle 
with the branches of trees hinder, of course, their 
growth, but, owing to their beauty and the value of 
their fruit, their presence is not so odious. It is 
quite otherwise with the poison ivy (Rhus toxicoden- 
dron) which firmly clasps the roots, trunks, and 
branches of trees, and is poisonous to the touch. The 
swamp sumac (Rhus venenata), which is a shrub, and 
often almost a tree, is abundant, and is also poisonous, 
causing a distressing dermatitis, which is often accom- 
panied by serious illness. Another class of extremely 
disagreeable weeds are the climbing, prickly briers of 
the genus Smilax. The most provoking feature of 
these weeds is that when their rhizomes have once 
gained possession of the soil, it is well-nigh impossible 
to eradicate them. Clothing and skin are torn in 
handling them, burning only causes them to sprout 
with fresh vigor, and, if left alone, they soon reach 
the tops of trees, to which they become inextricably 
attached. The only way to get rid of them is to cut 
them down with a bush-hook or machete, and then 
with a grub-hoe dig up their rhizomes, -bit by bit 
and year after year, until their extermination is com- 
