DANGEROUS INTERNATIONAL FOREST TREE DISEASES 39 



are carefully guarded. The use of an exotic pathogen, or even of an 

 exotic strain of a native pathogen, for inoculation purposes is a patho- 

 logical crime of grave significance. 



There is also room for research on the means of transmission of tree 

 diseases over long distances, though this is of less permanent value 

 than work on disease behavior. Too little is known about the relative 

 importance of different means of transmission. In particular it would 

 be valuable to have more evidence on the importance of seed as a means 

 of transmission. 



Evaluatory Action 



Any increase of knowledge of the distribution of diseases and of 

 their behavior on different hosts in different climates is of great as- 

 sistance in evaluating their importance, both present and potential. 

 If more facts were available on the actual and potential economic 

 losses inflicted by diseases transported from one area to another, 

 there would be more reasoned support for expenditure, either on 

 means to prevent their spread or on the mitigation of damage once 

 they had done so. In the past there has been a tendency to behave 

 as if all damaging diseases were of equal importance, at any rate 

 as far as restrictions of spread is concerned. It might be better if 

 our energies were concentrated on the restriction of a limited num- 

 ber of diseases, leaving others to spread more or less unhampered, 

 either because they were easily controlled or avoided, or because there 

 was good evidence that they would not be seriously damaging. How- 

 ever, selective action of this kind would be possible only on the basis 

 of much greater knowledge of disease behavior than we yet possess 

 for most forest pathogens. It can therefore only be practiced when 

 much more work has been done on what might be termed "interna- 

 tional disease behavior/' 



Practical Possibilities 



It is apparent from what has been said above that the amount of 

 work required to build up a knowledge of disease behavior, suffi- 

 cient to form a basis for international action is very great indeed. 

 The limitations on this work are primarily those of staff. At first 

 sight the most important limitation is the absence of forest patholo- 

 gists in many countries, but the very small number in most other 

 countries, particularly European countries, is equally serious. In 

 many cases, the workers are so few that their energies must inevi- 

 tably largely be devoted to immediate forest pathological problems. 

 They have little time to spare for investigations which are not of im- 

 mediate practical value or which are designed with long-term inter- 

 national, rather than immediate national, ends in view. Most govern- 

 ments take the view that forestry, earning as it does low rates of 

 interest, cannot support a high expenditure on research. And thus 

 they expect any substantial increases in research expenditure to be 

 clearly linked with resultant economic advantages. Economic ap- 

 praisals of disease losses, and in particular of the relation of research 

 costs to the prevention or mitigation of these losses, are thus obviously 

 desirable. Only thus can a reasoned case be stated for increased ex- 

 penditure on pathological research. 



In the meantime, any schemes for international cooperation must 

 either take full account of the limitations which the preoccupation of 

 forest pathologists with their local problems imposes, or else allow 



