62 THE PI.ANT WORLD 



Most of the information here gfiven was obtained from Strasburger's 

 " Lehrbuch der Botanik," but the subject was suggested by seeing some 

 peculiar lumps on the trunks of beeches. There seemed to be no especial 

 reason for their presence until it was noticed that nearly every one had 

 either a dead twig protruding from it or showed some sign to indicate 

 that one had been there. It is evident that a dead branch is in reality a 

 serious kind of wound, for the decaying wood is in such close connection 

 with the main stem that there is great danger of the infection being com- 

 municated to the whole plant. When the dead branch breaks off close 

 to the trunk the problem is practically the same as when the bark is 

 injured, and new wood is formed around and over the stump and finally 

 encloses it. Many of the " knots " seen in lumber are simply these old 

 branches that were enclosed in this wa3^ They are darker than the 

 surrounding wood because the}^ were exposed and had begun to decay. 

 The lumps on the beeches showed what efforts the trees were making to 

 cover the tiny dead branches. In some cases they were so successful 

 that there was nothing on the surface to show that a twig was underneath. 

 But when they were cut open it was all plain enough, and a little search 

 revealed all stages, from twigs not yet buried to those with the tip still 

 showing and then the final step when all trace was gone. In the course 

 of time the knobs disappear, and there is nothing to show that they had 

 ever been there, except when we cut into the wood and see the " knot." 



The beech is a tree whose branches are very responsive to light . One 

 close in to the trunk will often grow only a small fraction of an inch each 

 year, while another at the end of a prominent branch in the full sunlight 

 may grow a foot or more in the same time. The winter bud-scales of 

 the beech leave ring-like marks around the twig when they fall off, and 

 by these we can tell the age of the branch. They are most conspicuous 

 on the under side of the twig, for they seem to disappear sooner on the 

 upper side, probably on account of the slightly more rapid growth there. 

 Occasionally a twig scarcely a span in length will represent the growth 

 of a quarter of a century, but this does not give a correct idea of the age 

 of the tree, because most of the growth of the latter is at the top, where it 

 has enough light. No doubt the twig started to grow when the tree was 

 quite small, and it would be of interest to cut into the trunk of some 

 dead tree to see just how far we can trace the branch. The main point, 

 however, is that it is in an unfavorable situation, and in time succumbs, 

 and at last breaks off. When the stump is short the tree has little diffi- 

 culty in protecting the wound in the way already described. The longer 

 stumps are the cause of the formation of the lumps seen here and there. 



The beech is not the only tree that gets rid of its superfluous branches, 

 though we do not often see trees with such knobs as we have described. 

 When a tree grows in the open it may have low branches in a healthy 



