PROPAGATION BY ROOTS 165 
Some trees, like the Black Locust and Silver-leaved Poplar, 
are troublesome because of the readiness with which sprouts 
spring up from the roots. Some of the weeds, such as Canada 
Thistle and Field Sorrel, spread by developing new plants from 
buds on their spreading roots. When the Dandelion is cut off 
several inches under the ground, it often grows up again from 
the portion of the root left in the ground. 
