§ XIV.] Diseases in plants. 1 79 



ments, it may perhaps only play a secondary part as a saprophyte 

 in consequence of injuries produced by other causes. 



The latter supposition is partly founded on the phenomenon 

 of wet rot in potatoes, which has been closely examined by 

 Reinke and Berthold. It appears from the observations of 

 these authors, that the proximate cause of the phenomenon is 

 the development of Bacteria ; Bacillus Amylobacter is shown by 

 the descriptions to be present, and perhaps some other forms. 

 The wet rot usually attacks tubers which have been previously 

 sickly, that is, have been partly destroyed by a purely parasitic 

 Fungus, Phytophthora infestans. The rot does indeed attack 

 the tissue which had been spared by the Fungus and is still 

 alive, but it nevertheless is only a secondary phenomenon. At 

 the same time the rot appears in potatoes which have not suffered 

 from Phytophthora, though this is exceptional ; and the above- 

 mentioned observers succeeded in producing wet rot in healthy 

 potato-tubers by inoculating them with their Bacteria. This 

 agrees with a recent experiment of van Tieghem, who succeeded 

 in entirely destroying living tubers by the introduction of Bacillus 

 Amylobacter into their inner substance, and by keeping them 

 at the same time at the high temperature of 30° C. The same 

 results were obtained with the seeds of beans, stems of Cacti, &c. 

 In other words, these facts show that saprophytic Bacteria may 

 also, under special conditions, attack the tissues of living plants 

 as facultative parasites, produce disease in them and destroy 

 them. But this only confirms what was said above, that Bacteria 

 are not objects of great importance as contagia of diseases 

 affecting plants. 



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