90 PORTY-FIRST AnNUAL RePORT ON THE 



some degree from tlie decay whicli takes place around the spikes and 

 under the rails, from the fact that the iron in contact with this 

 wood neutralizes its natural antiseptic. The ends and centers of 

 chestnut ties are sound after the rails have cut into the wood enough 

 to necessitate their removal. The opinion is quite prevalent that they 

 do not decay, but are mostly destroyed by mechanical abrasion; which 

 is not the fact, for the microscope reveals the truth, the presence of 

 the mycelium of a fungus and its destructive work on the wood fibers 

 as an important reason of their rapid abrasion. 



The chestnut is lighter than the white oak and many of the wood 

 fibers much coarser, which enables it to be impregnated with an anti- 

 septic quite readily. The large ducts of the tAvo woods are about 

 the same size. The medullary rays of the chestnut are fewer than 

 of the white oak, and it is, therefore, more easily indented as a tie. 



The fungus which principally attacks the white cedar, G hamcBcypai'is 

 sphceroidea, Spach., is Agaricus campanella, Batsch. It even attacks the 

 growing tree, and in most cases its mycelium is found in the ties 

 when cut. The tree is a very slow grower and, as the lower limbs 

 become shaded, they die and are attacked by their special fungus, and 

 this communicates with the upright cells of the tree. It takes from* 

 ten to twenty years before the limbs break off and the wound or orifice 

 is closed by the growing Avood. As long as air has access to the 

 mycelium it slowly grows and destroys the Avood above and below the 

 wound, the decay spreading laterally ver}^ slowl}^, owing to the small 

 medullary rays and the preservatives they contain. As soon as the 

 orifice is closed, shutting off the air supply, the decay for the time 

 is nearly if not entirely checked. When the trees are cut for ties it 

 is not uncommon to find one or more decayed spots, from one-half to 

 an inch in diameter, extending nearly the entire length of the tie. 



The durability of the wood is so great that such ties are not 

 rejected as long as there is sufficient sound wood for spiking. This 

 wood contains a natural preservative and is very durable in contact 

 with the soil, but its structure is too light and delicate to long with- 

 stand the heavy traffic of trunk lines, though from its durability it is 

 valuable for those of moderate traffic. 



The fungi which destroy ties made of Tamarack, Larix Americana, 

 Mx., are Polyporus p)vnicola, Fr. and Trametes Pint, Fr. 



The fruit of the former always shows traces of phosphoric acid. 



This wood is heavier than white cedar, the Avood cells being larger, 

 with thicker walls. It is also much stronger because the cells in the 

 annual layer formed in the autumn are nearly solid and in sufficient 

 number to resist indentation or cutting of the ties by the rails under 



