172 Our Field and Forest Trees 



So when, later, someone takes pity on the poor 

 tree and cuts its bonds, there is a raised band left 

 around the trunk. 



The swellings which we call " tumors " are also 

 caused by some interference with the natural move- 

 ment of sap. They are places where the tree was 

 once wounded or broken or attacked by some fun- 

 gus or insect enemy, or where, perhaps, some 

 young branch was torn away. When this happens 

 to a strong healthy tree a great quantity of sap 

 flows at once to the injured part, and the result is 

 a swelling or sometimes a huge lump. 



Cabinet-makers call a swollen mass like this a 

 " burl," which is the old English word for a knot 

 in cloth. The inside of large " burls " is often 

 found to be very beautiful. The lines of the wood 

 are twisted all through, and sometimes they will 

 coil and curve into lovely patterns. 



We have said that the bark of trees is unlike the 

 skin of animals in this, that it does not stretch 

 when the body beneath it grows, but has to be, by 

 little and little, torn off. This constant tearing and 

 stretching has caused the deep furrows which we 

 see in the bark of the older logs. But sometimes 

 the bark of garden and orchard trees becomes so 

 dense and strong that it will not tear, and so the 

 trunk beneath it cannot expand. A tree in such 

 case is said to be " bark-bound." Such trees are 

 sometimes unable to develop, though they are 

 rooted in rich earth and getting the best of care. 



