WOODS AND THEIR DESTRUCTIVE FUNGI 44.3 



white-oak ties. It is usually dimidiate, as shown in Fig. 9, though, 

 when growing upon the under side of timber above-ground, it is often 

 resupinate ; the pores all point downward, the substance of the cap is 

 hard, and, if undisturbed, the pores in the next year's growth form 

 over that of the preceding years, but, en- 

 larging the area, many of them are found 

 twelve to eighteen inches across, and by 

 cutting through them so as to show the y^jISM? 3 ^ |t J y 

 section, six to eight years' growth is often 

 seen. In this figure but one year's growth jj 

 has taken place ; frequently two caps form 

 instead of only one, as here shown. 



In white-oak timber and ties the earlier S^ 



growth of the mycelium is not as contin- Fia 9 --** appianatus (Pr.). 



uous and uninterrupted as in the yellow pine, but grows more in little 

 white patches, with considerable wood intervening between each. In 

 Fig. 9 they are shown as dark spots. The massive bundles of medul- 

 lary rays of this wood slowly decay, and preserve their form long 

 after the other tissue has decayed. The large ducts seen in Fig. 3 are 

 not open with a free communication, but filled with a delicate tissue, 

 remains of which are visible in the cut ; this tissue will be found quite 

 perfect in ties well advanced in decay. 



The fungi so far illustrated in this paper apply mostly to the decay 

 of timber under conditions similar to those of railroad service. In the 

 next paper I shall give two or three illustrations of fungi of more gen- 

 eral character. To deal with the great practical question of preventing 

 wood from decay, the subject requires a more special treatment than 

 it has received. Each species of tree, to a great extent, has special 

 fungi, as it has insects which are not common upon other kinds of 

 wood. Red cedar, cypress, locust, and catalpa are very durable in 

 contact with the ground, where some others would quickly decay. 

 The chemical composition of woods is not practically the same, as re- 

 cently stated, but differs even in the sap- and heart-wood of the same 

 species. Some of the woods have compounds in their cells easily 

 induced to decompose and start the wood-tissue, while others have 

 different compounds requiring inducing agents of greater intensities 

 to begin decay ; and it is not true that a fungus which will destroy one 

 wood will destroy all of the other species, and this one fact is of great 

 practical importance, for, in a road-bed filled with the mycelium of one 

 kind of decayed wood, another wood may be used which is not affected 

 by that fungus, and its mycelium would be inert. 



In treating wood it is found that the chemical which will prevent 

 the germination of the spore of the fungus may not protect it from 

 the attacks of its mycelium, contained in the ground or upon other 

 decayed timber. 



Experience has long since established the fact that wood kept per- 



