PLANT PATHOLOGY—JONES, 409 
But although De Bary’s work has settled for all time that the 
parasite is an independent plant entering the host from without and 
feeding upon it to its destruction, we must not forget that the more 
fundamental problems of parasitism remain with us. In biology, the 
definition is always dangerous, and the more complete and finished 
the more the danger. De Bary’s classification of all fungi as parasites 
and saprophytes, obligate and facultative, is so complete and satisfy- 
ing that it is constantly misleading. De Bary thought as the mycolo- 
gist with attention focused upon the fungus. The first concern of the 
pathologist must ever be with the host plant, and chiefly with the 
host plant under conditions of culture. _He must constantly be alert 
to the fact that parasitism is not a fixed but a fluctuating relation, 
dependent as to its occurrence and degree upon a complex of condi- 
tions, and these involving the reactions of not one but two widely 
different organisms. Although the fact of parasitism was settled 
and the modern science of plant pathology securely based upon it, 
there has been no time since when phytopathologists realized as 
clearly as to-day the importance of the problems yet to be solved in 
this field. We have scarcely begun the study of the intimate relations 
of parasite and host, the conditions and results of parasitism. 
III. THE LIFE-HISTORY PROBLEMS. 
The fact of parasitism accepted, the problem of the life-history of 
the parasite at once presented itself to these early students. Kihn’s 
work on grain infection by smut (1858) and De Bary’s upon the life 
histories of the Peronosporales (1863) with proof of heteroecism of 
the rusts (1864-65) set the pace. In the retiring address of my 
predecessor, we learned how Farlow brought to this country the 
coals which have kindled the fires of our best American research in 
mycological pathology. 
It should remain the first concern of plant pathologists that this 
work be continued. Discoveries as to life histories of parasites are, 
in the long run, of more practical importance as fundamental for 
disease control than demonstrations with spray mixtures. The‘lat- 
ter are usually transient contributions, the former permanent. It 
is, therefore, of good promise that the two life-history problems 
which first engaged De Bary’s efforts, those of the grain rust and the 
potato fungus, are to-day held more open and are receiving more 
earnest attention than when De Bary died. It is well that the prob- 
lem of the overwintering of the apple scab is no sooner settled by 
one investigator for one locality than it is opened by another, work- 
ing in a different environment. Life-history problems have so many 
variations and complexities that they must ever remain with us, and 
progress in their fuller solution will continue as one index to general 
progress in plant pathology. 
1 Farlow, W. G.., loc. cit. 
