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UNITED STATES DEPARTMENT OF AGRICULTURE 
Bureau of Entomology and Plant Quarantine 
Washington, D. C. 
EXPLANATORY STATEMENT 
Re: Plant disease reference and study material, 
Sumniaries of readily available information regarding 
plfimt diseases which are responsible for specific foreign plant 
quarantines and of other diseases which may appear to be of special 
interest to those engaged in enforcing the foreign plant quarantines 
are being prepared as time permits. 
Information, if available, will be given under a fixed 
set of headings in uniform order but there will be no attempt to 
make the treatment uniform, at least at this time. Any great stress 
on uniformity or on an exhaustive euid critical analysis of the 
literature would mean years of further delay in issuing the 
summaries. After the series is completed it should be possible to 
revise the write-ups bringing them up-to-date again, making any 
desired corrections and making them more nearly imiform. 
In using the summaries the reader should remember that 
most pathogens are variable, that their hosts are variable, that the 
weather and climatic conditions under which the pathogen and host 
develop are variable and affect both host and pathogen, and that 
observers vary in their interpretation and recording of data. 
Furthermore the reviewer is subject to error in his endeavors to 
combine data from various workers in different parts of the world 
into a brief summary. 
The bibliographies are designed to include a few more or 
less general studies of the disease covered and in some cases studies 
of special phases or items of information of special interest under 
some one of the outline headings. Some of the notes following 
citations indicate the nature of the work covered in the article, 
others give bits of information based on the article. Divergence of 
views of different authors will be found in the notes at times also* 
These notes are largely copies of rough notes made when the articles 
were reviewed and are likely to be limited to a few interesting items 
which may not be representative of the article as a whole but 
appeared to be useful in rounding out the general picture. 
