1896.] The Bacterial Diseases of Plants. 627 
may turn out to be only secondary, appearing as a saprophyte 
in consequence of injuries previously received.” Concerning 
the wet rot of potatoes he states that ordinarily it is a second- 
ary phenomenon following the attacks of the parasitic fungus 
Phytophthora infestans, but admits that exceptionally potato 
tubers may become wet rotten without the presence of Phy- 
tophthora, and that “the above named observers succeeded in 
producing the appearance of wet rot in sound potato tubers by 
inoculations with their bacteria; in agreement with which 
stands a recent experiment of van Tieghem, who succeeded in 
totally destroying living potato tubers by means of Bacillus 
amylobacter when he introduced this into the interior of the 
tuber and maintained the same at a high temperature (35°).” 
In the second edition of his Lehrbuch, published in 1889, Dr. 
Hartig modified his statements somewhat, expressing essential- 
ly the same opinions as de Bary. The yellow rot of hyacin- 
ths is recognized as a bacterial disease, although rather doubt- 
fully in as much as it is said not to attack sound, well-ripened 
bulbs, under normal conditions, but only when they have 
received wounds or been attacked by fungi, especially by a 
hyphomycete which is said to be an almost constant accom- 
paniment of the rot. The wet rot of potato tubers is admitted 
to the list, but with the statement that it is mostly a secondary 
matter, following the rot of stem and cells due to Phytophthora 
infestans. One other bacterial disease is mentioned, viz., pear 
and apple blight, with the suggestion, however, that it may 
have been erroneously attributed to bacteria, since the fungus 
Nectria ditissima produces in the bark numerous little bacteria- 
like gonidia. 
Such was the general opinion on this subject down to within 
less than a decade. Even to-day the majority of well educated 
botanists would find nothing to contradict in the statement that 
there are very few diseases of plants distinctly attributable 
to bacteria. As a matter of fact, however, there are in all proba- 
bility as many bacterial diseases of plants as of animals. 
Various explanations have been advanced to account for this 
freedom or supposed freedom of plants from bacterial parasit- 
ism. As we have already seen, de Bary was inclined to ascribe 
