716 A NATIONAL PLAN FOR AMERICAN FORESTRY 



The introduction of dangerous organisms is not limited to the 

 bringing in of new species. It is now well known that our most 

 important fungous species consist of numerous strains, some of which 

 differ from others very clearly in their virulence. For example, the 

 well known root-rot fungus Fpmes annosus is common throughout 

 both Europe and North America. In the Douglas fir in the Pacific 

 Northwest it is very frequently found, but appears to be unimportant 

 so far as parasitic activity is concerned. In Europe, on the other 

 hand, it is an extremely serious parasite in planted forests and causes 

 heavy damage to European plantations of our own Douglas fir. 

 There is reason to believe that some of the European strains of this 

 root-rot fungus are more dangerous than any of those which we now 

 have; their importation might prove serious, particularly for our 

 reforestation projects. 



Introduced diseases must be found, studied, and if possible eradi- 

 cated while they are new in this country. Delay may mean their 

 escape beyond control. To permit infectious material to remain 

 undisturbed for study in our forests or among shade trees is mani- 

 festly unsafe. The knowledge of the disease, its methods of spread, 

 and the vulnerable points in the life history of the casual organism, 

 essential for effective eradication, can be acquired safely only by 

 studies abroad in the countries where the disease is already established 

 and these studies need to be carried on at the earliest possible moment 

 after the discovery of a disease in America. In the cases of virulent 

 diseases known to exist abroad and to be able to attack trees related 

 to our forest species, but which have not yet gained entry into 

 America, it is the part of wisdom to conduct preliminary studies in 

 the foreign countries to get information that will enable us to prevent 

 or at least to delay as long as possible their introduction here. The 

 Dutch elm disease is an example of a case in which studies abroad 

 are needed. At the present moment no one can answer the question, 

 How did the elm fungus reach America? We cannot know just how 

 to quarantine or where to expect additional outbreaks and combat 

 them intelligently and effectively till this question is answered. 



Troublesome diseases may be introduced from other parts of our 

 own country as well as from abroad. While it is possible that most 

 of the dangerous fungi native .to this country are already present in 

 every part of the continental United States in which there is any 

 common native host that is particularly susceptible to them, this is 

 by no means certain. A fungus living harmlessly on the outer bark 

 of eastern hard pines has been proven able to cause severe damage to 

 Douglas fir in the East. This tree in its natural range would probably 

 be more resistant to the fungus; but if the fungus should reach the 

 western forests and should there prove able to attack this most im- 

 portant species as it does in the East, we would have a forest calamity. 

 An example of danger from the movement of native diseases in the 

 opposite direction is afforded by the dwarf mistletoes of pine. Prob- 

 ably the most important of the growth-reducing parasites, they are 

 now limited to the West, and are separated from the eastern pine 

 stands by a belt of prairie hundreds of miles wide along the hundredth 

 meridian. These mistletoes are not spread by the wind as are the 

 fungi and can establish themselves in a new place only if both sexes 

 are introduced. It is probable that the eastern conifers have never 

 been exposed to them. Artificial inoculation experiments in neutral 



