22 2 TRANSACTIONS OF ROVAL SCOTTISH ARBORICULTURAL SOCIETY. 



tions, in trees of very various types and ages, tended to suggest 

 the appearance of a new factor, such as the calcination afforded, 

 rather than the cumulative effect of a series of minor causes, 

 such as unfavourable soil, overcrowding, unsuitable climate, 

 and so on. Further, the respondent brought forward a large 

 body of expert opinion to controvert the statement that the 

 observed damage could be ascribed to the attacks of insects 

 and fungi. It would not appear that there was evidence of 

 very extensive insect attacks, and therefore much of the expert 

 evidence dealt with the question of fungoid attack. 



The subject is of especial interest, because it will be 

 recollected that at this date (1881-2) the subject of symbiosis 

 had not been so thoroughly worked out as it was later. It 

 was known that fungoid mycelia did occur round the roots of 

 forest-trees, and that in some instances these fungi were patho- 

 genic. On the other hand, it was not known that certain of 

 the observed mycelial threads form what we now call mycorhiza, 

 which is absolutely beneficial, enabling the tree to take 

 advantage of the humus of forest-soil. The absence of this 

 knowledge led to much wrangling among the expert witnesses, 

 some of whom declared that the mycelial threads always meant 

 the possibility of disease, while others emphasised the fact of 

 observation that such mycelia could be shown to occur on the 

 roots of perfectly sound trees. Much of this evidence is of 

 value as showing how much progress in our knowledge of the 

 conditions of plant life has been made in a period of less than 

 thirty years, a fact which is full of promise for the future. 



We shall give some account of the chief lines of evidence 

 brought forward by the botanical experts. As was natural 

 under the circumstances, the number of such experts brought 

 forward by the respondent — who was constrained to prove that 

 no other cause for the observed damage existed except that 

 of the fumes — was much greater than that brought forward 

 by the appellants, who laid greater stress upon the chemical 

 difficulty of proving that the fumes had actually reached the 

 affected trees. 



The exact appearance presented by the trees in the 

 plantations may be briefly noted. The first effect of the 

 fumes was to produce a drooping appearance, as if the trees 

 were suffering from want of water. This was followed by a 

 change of colour in the leaves, which lost the green tint of 



