viii PREFACE 



Another aim has been to establish the biological relation- 

 ships of the pathogenic organisms dealt with; and I trust 

 that readers who are trained in the biology of cryptogams 

 will condone the verbal and ideal stumblings of a beginner ; 

 and that others, to whom the matter of this part of the book 

 may be as new as it was to the author two years ago, will 

 follow with sympathy and some profit the progressive, if 

 limited, illumination that has been attained. 



In order to make this attempt possible, it has been 

 necessary for me to consult literature outside that contained 

 in our professional libraries, and I am under particular 

 obligation to the officers of the library of the Linnaean 

 Society of London, and of the Cryptogamic Botany Depart- 

 ment of the British Museum. Both for direct information 

 and for guidance in the choice of literature Mr. J. Rams- 

 bottom's articles in the " Transactions of the British 

 Mycological Society " have been indispensable to me. 



My indebtedness to colleagues and others who have 

 assisted me with gifts of material and specimens is acknow- 

 ledged in the text, but I must make additional reference 

 to the skilled help generously given me by Dr. J. Herbert 

 Perkins, pathologist to the Hampstead and North-West 

 London Hospital. 



J. JACKSON CLARKE. 



LONDON, September, 1922. 



