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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. 
Finally, there is culturing 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 parasites 
on the other — both things of paramount importance in plant pathology, 
scientific and economic. Success in such work is conditioned upon 
our ability to control and interpret environmental conditions. When 
the superiority of the greenhouse for such studies is more fully realized, 
we shall here work out the most of our fundamental 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 in 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 supremacy 
rests here, thanks to the high ideals and energetic — at times militant — 
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 forty years ago, no American worker 
has doubted the occurrence of bacterial diseases of plants. That 
Europeans 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 
^1 Pinoy. Role des bacteries dans le developpement du Plasmodiophora bras- 
sicae. Compt. Rend. Soc. Biol. 58: loio. 1905. 
