168 Our Field and Forest Trees 



On the ends of the largest logs, the outermost 

 rings are smaller than those nearer the center, for 

 as a tree grows older, the layers of new wood 

 made each spring under its bark are thinner and 

 thinner. A Douglas spruce a thousand years old 

 has outer rings no thicker than tissue paper. In- 

 deed, some very old trees form rings so small that 

 one cannot count them without a hand-lens. Dur- 

 ing its last years a tree has scarcely strength enough 

 to build new tissue. 



The timber diseases which foresters fight attack 

 the sickly and the aged trees. So lumbermen say 

 that old wood is undesirable, or actually useless, 

 for many practical purposes. 



If we take from the woodpile an oak stick which 

 has been sawed lengthwise, and polish it with 

 sandpaper, we shall see that it has a flaked ap- 

 pearance. These flakes are the " silver grain " — 

 the little streaks of pith, left among the harder 

 wood-cells. 



We have learned that the living tree uses these 

 pith-rays as larders, and stores in them nourish- 

 ing starches to feed the opening buds of spring. 

 When a fungus spore gets into the wood of a tree, 

 and begins to grow there, this nourishment gives 

 aid and comfort to the enemy. The spore, when 

 it begins to grow, puts out little white threads, 

 which stretch and feed along the pith-rays first; 

 thence they penetrate the firmer wood-cells. 



If a tree has been chopped up and put into the 



