204 SCIENCE PROGRESS 



to believe that in certain obscure diseases which appear to 

 indicate a bactericidal origin perfected methods of research will 

 yet discover the suspected organism. 



It is impossible to do more than briefly indicate the 

 characteristic features of attack in a few cases which have been 

 worked out ; it will be understood that no attempt is made to 

 present a complete account of all the bacterial parasites which 

 have been recorded. 



In addition to their role of parasites, the bacteria function 

 very actively as saprophytes, following in the wake of parasitic 

 fungi and completing their work of destruction ; this observa- 

 tion has no doubt led to the scepticism as to their aptitude 

 as true parasites. Thus in discussing the disease of the potato 

 (1898) Ward, while disclaiming any implication that no bacterial 

 disease existed, expressed the conviction that alleged cases were 

 not convincing and showed " that the way into the tuber is 

 prepared for bacteria by fungus hyphae and the open passages 

 of destroyed vascular bundles afford them ample space." This 

 last statement is incontestable ; it is but natural to expect that 

 bacteria should be present in many fungoid plant-diseases, and 

 that their part is only secondary may be true in certain cases, 

 but undoubtedly the converse is also true, viz. that the bacteria 

 are often the prime agents in paving the way for the fungus 

 hyphse. In cases where bacteria and a fungus are associated 

 together in a plant-disease, it is necessary to isolate these 

 organisms and grow them in pure culture. As regards the 

 bacteria, modern methods of culture have rendered this a fairly 

 easy task, but to obtain the fungus free from any bacteria is a 

 matter of the utmost difficulty. The definition of a pure culture 

 in the case of fungi must be extended. It can no longer mean 

 that no other fungus is present but must include the conception 

 that bacteria are also entirely absent. 



A promising field of inquiry awaits the investigator into the 

 relation between bacteria and fungoid parasites and their 

 association one with another in plant pathology. In the disease 

 known as Finger and Toe, bacteria are always present in 

 conjunction with Plasmodiophora, and hitherto, I believe, a 

 culture of Plasmodiophora free from bacteria is unknown. 

 Pinoy considers that they play an active part in this disease. 

 The parasitism of Fiisariiim affords a further illustration. A 

 species of Fusarium commonly met with on turnips and swedes 



