340 Forestry at Nurnberg Exhibition, [sept., 



thoroughly air-dried, and is then immersed in the solution. 

 The water of imbibition, which is in the substance of the cell 

 walls, is expelled and replaced by the solution. 



Impregnation by Filtration, where the solution is stored in a 

 tank at a higher level than the stem to be impregnated, to 

 which it is led by a pipe which is closely fitted into a hole in 

 the wood. In this case the solution is under pressure, and is 

 thus forced into the wood. 



Impregnation by Injection, where the wood is first artificially 

 dried and is then placed in a steel chamber, from which air may 

 be pumped, and into which the solution is introduced under a 

 pressure of several atmospheres. This is the method usually 

 adopted on a large scale in this country. 



As is well known, different species of wood absorb fluids very 

 differently, the least suitable for impregnation being those with 

 a well-marked duramen. The difficulty in forcing fluids into 

 such wood is due to the fact that their vessels are packed full of 

 a cellular growth {tJiyloses), as may readily be seen through a 

 microscope of moderate power. 



As was to be expected in a national exhibition in the country 

 in which Hartig laboured for many years, and where Tubeuf 

 n^w holds the chief professorship of Forest Botany, the diseases 

 of wood, living and dead, are illustrated by a wealth of material 

 never before equalled. Perhaps the most interesting object in 

 this sub-section is the model of a dry-rot chamber, the original 

 being at Bernau on the Lake of Chiem in the Bavarian High- 

 lands, some two hours by rail from Munich. The quality of 

 timber is tested in many ways, by resistance to pressure, resist- 

 ance to tension, specific gravity, &c. But for many purposes 

 the important thing to determine is resistance to decay, and 

 Tubeuf has hit upon a novel and efl"ective way of applying 

 this test in a reliable and fairly rapid manner. For this 

 purpose he has had a wooden hut erected in a peat bog, 

 thus ensuring that it shall always be fairly moist, and into this 

 house he has introduced a supply of old wood which is full of 

 the dry-rot fungus. In order to test the power of resistance to 

 decay of any species of wood, or of wood treated by any special 

 preservative method, he places blocks of a given weight within 

 reach of the fungus, and in a few months, or a year or two at 



