INTRODUCTION 5 



systematic, morphological, and physiological standpoints. Too often, 

 in the early work, the chief object of the study has been to identify 

 the fungus associated with a given disease and to describe its fruit- 

 ing stages. An investigation of the fungus, however, should include 

 an account of its complete life history wherever possible, the rela- 

 tions of the fungus to conditions under which it is injurious, the 

 character of the growth produced upon various culture media (when 

 the organism is culturable), the conditions under which fruiting 

 stages may be developed, etc. In the course of time, therefore, it 

 will be necessary to repeat much of the work of earlier date, which 

 has seemed to be more or less complete. 



Anatomical effects. The anatomical study, in the sense in which 

 it is here used, will be concerned with the relations of the host to 

 the parasite, in so far as the former may be modified in growth or 

 minute structure. All lesions, hypertrophies, or other structural 

 changes produced in the host plant are worthy of the closest atten- 

 tion. These changes in the host are most diverse, varying, on the 

 one hand, from minute modifications of a single cell, or of a small 

 group of cells, to those changes of form which involve an immense 

 increase in the size of the host organism, often giving rise to rela- 

 tively enormous deformities, such as may be noted in the case of 

 the club root of cabbage, plum pockets, cankers, and smut of corn. 

 Again, the deformities may result in the pushing into growth of an 

 abnormal number of buds, in many instances accompanied by de- 

 creased size of the branches and changes in the trophic relations, 

 such as to develop the various forms of witches' brooms. The 

 anatomical changes 1 in the host are those most commonly termed 

 pathological changes. Unfortunately these are often discussed as 

 if they were the only pathological effects. They are, at any rate, 

 the chief evident pathological effects in many cases, and for that 

 reason they constitute in the popular view that which is properly 

 designated " plant pathology." 



Physiological relations. In close connection with the anatom- 

 ical changes produced in the host, a study should be made of the 

 physiological relations of host and parasite, particularly of the 



1 Kiister (Pathologische Pflanzenanatomie, 312 pp., 121 figs., 1903) has at- 

 tempted a general classification of anatomical modifications induced by diverse 

 stimuli. 



