234 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 
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 (¢hyloses), 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 
now 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, etc. But for many purposes 
the. important thing to determine is resistance to decay, and 
Tubeuf has hit upon a novel and effective 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 
most, definite information as to the rate of destruction can be 
obtained. 
A number of cross-sections exhibit the inexplicable con- 
dition of things that growth is more rapid on the under side than 
on the upper side of the branch of a conifer, whereas in the 
