It is claimed that this would yield valuable information on the likely effect of the organisms if transferred elsewhere on to new hosts. This is the main advantage claimed, and examples, such as the spread of Cronartium ribicola , are quoted as catastrophes which might have been prevented had such information been acted upon. Other advantages claimed are the use which other forest disciplines, such as mensuration or genetics, could make of such plantations. The disadvantages are serious, and have been emphasized by all who commented on the scheme. The intrinsic difficulties comprise adequate sampling of large areas in order to expose a species to the full spectrum of possible diseases, the difficulty of forecasting how an organism will behave in a changed environment, and catering for unknown or apparently harmless organisms which may become important elsewhere.
Practical difficulties are no less formidable.
The most valuable information would accrue from the most pathologically unexplored regions - precisely where plantations would be most difficult to initiate, supervise and inspect. There might be difficulties over finance - particularly where one country had to carry out plantings for the benefit of another. There would certainly be difficulty over adequate supervision and inspection by trained pathologists. All who commented on the scheme emphasized the need for first assembling all relevant data from two sources. It is doubtful whether in any country such existing exotic plantings are regularly surveyed for disease.