1911.] PUBLIC DOCUMENT — No. 31. 41 



would have developed and occupied the space given up to the 

 treated fibers; and probably in all cases a large number of the 

 roots would have penetrated through the bottom of the pots into 

 the water below. In only a very few instances did any of the 

 roots in the experiments where creosote was used penetrate to 

 any depth where sawdust and excelsior were used. Practically 

 all the penetration occurred close to the surface of the pot, where 

 the chemically treated fibers were packed rather loosely, and 

 especially in those experiments where excelsior was used. 



A more or less thorough calking of the joints of Akron tile 

 with either creosoted excelsior or sawdust would undoubtedly 

 prevent the occurrence of roots in the joints, and consequently 

 in the tile itself. Some sewer pipes have been calked with these 

 chemically treated fibers, but it is as yet too early to state how 

 effectually they may have accomplished their purpose. Akron 

 tiles, or those provided with flanges, are best adapted to treat- 

 ment. Ordinary land drain tiles, however, are not provided 

 Avith flanges, and it is a question whether root penetration could 

 be successfully prevented by using these fibers, at least by plac- 

 ing them loosely over the joints. It would be possible and no 

 doubt practicable, however, to clamp masses of treated asbestos 

 or excelsior around the joints of ordinary land tile, which would 

 prove effective. Such clamps could be constructed from heavy 

 galvanized wire, so as to hold the excelsior very firmly around 

 the joint, and at the same time not affect materially the inflow 

 of drainage water. It would be possible, also, to make use of 

 small sections of tile of larger diameter (collars), which could 

 be placed over each joint and the treated fibers packed in tightly 

 around the joints. 



Creosote appears to be the best substance with which we have 

 experimented, since it is not only one of the best preservatives, 

 but possesses excellent toxic properties. No doubt there arc 

 other fibers than those which we have used, and there are many 

 substances which possess properties toxic to roots, such as tannin, 

 etc. ; but many others, like sodium arsenate, wash out quickly 

 and lose their effectiveness in a short time. 



From the results of these experiments it would appear that 

 chemically treated fibers would undoubtedly remain for many 



