PLANT PATHOLOGY—JONES. 411 
And even the so-called obligate parasites deserve attention, for we 
are not restricted to artificial or dead media in pure culture work. 
The living sterile tissues of the proper host may be secured for many 
parasites providing only the need is sufficient to justify the pains- 
taking. This of course, is easy with many interior tissues of fleshy 
parts, while for various other plants the seedlings may be grown from 
sterile seeds. It would seem that the problem of whether or not 
Plasmodiophora brassicae is the sole cause of club root of crucifers, or 
whether association is necessary with bacterial or other organisms, as 
has been suggested,! is a challenge to such increased skill in culture 
technique. 
Vinally, there is culturmg upon the living host. Although this 
was the earliest method in vogue, and has yielded such gains especially 
in the hands of Arthur and others with rusts, yet the general applica- 
bility and importance of this practice in plant pathological investi- 
gations has not been fully realized. It is only thus that we can learn 
with exactness of related varietal or species susceptibility of hosts on 
the one hand and of the occurrence of biological forms among para- 
sites on the other—both things of paramount importance in plant 
pathology, scientific and economic. Success in such work is condi- 
tioned upon our ability to control and interpret environmental condi- 
tions. When the superiority of the greenhouse for such studies is 
more fully realized, we shall here work out the most of our funda- 
mental problems, with the field plat as the place more important for 
verification than for investigation. 
V.—BACTERIA IN RELATION TO PLANT DISEASE. 
The problems of bacteria im relation to plant disease naturally 
followed the advent of the pure-culture method. While, from the 
American standpoint, this is the most important chapter in the 
development of modern plant pathology, it is at the same time, to 
us, the most familiar. The universally acknowledged world suprem- 
acy rests here, thanks to the high ideals and energetic—at times mili- 
tant—leadership of him who two years ago was the honored president 
of this society. I may only outline certain things in order to warn of 
dangers or suggest other problems. 
Since the work of Burrill, over 40 years ago, no American worker has 
doubted the occurrence of bacterial diseases of plants. That Euro- 
peans were skeptical for a time was the natural consequence of too 
great reliance upon tradition and too great respect for authority. 
And as we grow older in the work in America we must realize that the 
traditions will soon be ours and that the paralyzing hand of authority 
will rest more heavily upon us. While in general we must follow its 
1 Pinoy, Role des bactéries dans le developpement du Plasmodiophora brassicae. Compt. Rend. Soc. 
Biol. 58° 1010. 1905. 
