1917] 
ZELLER—DURABILITY OF YELLOW PINE 95 
of the mycelium might result in an increased tension in the 
tissues, as may be the case in those forms of decay described 
by von Schrenk (’01, p. 204). Thus, coniferous trees should 
be pruned when young, at least before any heart-wood is 
formed, so that the resin will exude and cover the wound, 
since, as was demonstrated іп a previous paper (Zeller, 716), 
fungi will not germinate nor grow on pure solid resin as it 
exudes from the wounded bark or sap-wood. 
Hartig’s observations, referred to above, were made in the 
field. He states that in the summer of 1877 damage done 
by wind gave opportunity to study the aseptic influence of 
resin on wounds. In all cases of fracture there was exudation 
from the sap-wood but not from the heart-wood. He further 
noticed that where resin in the solid state is infiltrated in the 
cell walls and also fills the cell lumen the penetration of the 
fungous mycelium is mechanically hindered. 
Temme (’85) believed that certain kinds of wood are ren- 
dered more durable by a gum which is formed in wood exposed 
to air. This is especially true where active sap-wood is ex- 
posed as the result of a lesion. Bordering the active wood 
thus aérated a layer of ‘‘Schutzholz’’ is formed because of 
the infiltration of this gum, which, he believed, made the wood 
resistant to fungous attack. 
Dudley (’87) observed that longleaf pine (Pinus palustris) 
does not seem to be exceptionally durable when placed in con- 
ditions favorable to the growth of fungi, as in roadbeds as 
railroad ties. He states that ‘‘ordinary specimens of this pine 
contain from 18 to 20 per cent of resinous matter, which is 
supposed to add much to the durability of the wood. But this 
does not seem to be the case when the wood is put in the 
ground or in the roadbed as ties.’’ 
To Mayr (’94) we are indebted, probably more than to any 
other worker, for our present knowledge of the influence of 
resin on the durability of coniferous woods. He has made an 
extensive study of the distribution of resin in these woody 
tissues and also of the physiological importance of the resin 
to the tree, besides drawing quite definite conclusions as to its 
influence on fungous growth. 
