8 Forestry Quarterly. 



sent cannot account for the rapid penetration of gases and pre- 

 serving fluids. 



D. Penetration of Air Through Green Wood and Re-soaked Dry 



Wood. 



The observations of the writer confirm the statement of Tie- 

 mann that the spiral cracks when once formed do not close when 

 seasoned material is re-soaked. In view of this fact is is signifi- 

 cant that in many cases dry wood when thoroughly re-soaked is, 

 under moderate pressure, as impervious to air as unseasoned 

 material. Furthermore, although long pieces of green sapwood 

 are impervious to air, even under heavy pressures, short pieces of 

 the same wood, more than one fiber length long, may be pene- 

 trated easily and rapidly and by slight pressure. 



B. Weiss' Modification of Tiemann's Hypothesis. 



In a paper read before the American Wood Preservers' Asso- 

 ciation, Weiss* explains the greater penetration of creosote in 

 dense woods and in heavy "summer-wood" of long-leaf pine 

 paving blocks by the fact that dense tissue cracks more in, drying. 

 "Such splitting does not occur to the same extent in the light thin 

 walls, as they seem to yield and bend more under the readjust- 

 ment of the wood during drying. The heavy walls it seems, 

 therefore, cannot readily adjust themselves to moisture changes, 

 and consequently split somewhat in the manner of a tie when it 

 dries too rapidly." 



The objections to Tiemann's hypothesis which have been out- 

 lined above are equally significant in this case. However, as a 

 special test of this theory I have examined the wood of long-leaf 

 pine paving blocks in which the penetration of heavy creosote 

 and tar oils was confined almost exclusively to the dense bands of 

 "summer- wood." The secondary walls of the "summer-wood" 

 in the majority of cases were found to be unruptured. Fig. 7 

 illustrates a cross section of the "summer-wood" of a very dense 

 specimen of long-leaf pine. The heavy secondary walls are seen 

 to be devoid of drying cracks (Compare Fig. 4). Since greater 



*Weiss, H. F. Structure of Commercial Woods in Relation to the In- 

 jection of Preservatives. Proceedings of the Eighth Annual Meeting 

 of the American Wood Preservers' Association, 1912, pp. 158-87. 



