198 SCIENCE PROGRESS 



considerable space to the discussion of many well-known cases. 

 Migula's attitude upon this question is in great contrast to that 

 of Dr. Alfred Fischer at the same date. In the Voi'lesiuigcn 

 iiher Baktcricn (July, 1897) Fischer, in spite of the evidence 

 available, expressed complete disbelief in the existence of 

 bacterial diseases of plants. With the exception of the root- 

 nodules of Leguminosse, he professed to know of no single 

 instance where bacteria invadelthe closed, living cells of plants ; 

 he states that the uninjured plant is " quite impregnable to 

 their attacks." He maintained that bacteria live metatrophically 

 only in diseased plant-tissues " that have already been dis- 

 integrated and decayed by parasitic fungi." That the bacteria 

 may "assist these subsequently in their work of destruction 

 and modify perhaps more or less the character of the disease, 

 but except for injuries from frost or insects the first attack on 

 the plant is always made by fungi. All the cases of so-called 

 bacteriosis of plants from the 'gommose bacillaire ' of the vine 

 down to the 'schorf of the potato, are primarily diseases of 

 non-bacterial origin in which the bacteria are present merely 

 as accidental invaders." He even goes so far as to state that 

 " infected wounds are dangers that have no existence for 

 plants," owing to the development of wound-cork, which would 

 cut off the provision of moisture and supplies of nutriment to 

 the exclusion of the further progress of any pathogenic bacteria. 

 As will be seen later, the rapid destruction of the cells, due to 

 the activity of a bacterial parasite, as a rule precludes this 

 protective tissue being formed ; and the idea that fungi are 

 always responsible for the primary attack is not in accordance 

 with the cases described in which no trace of a fungal hypha 

 was present. It is not possible here to enter in detail into 

 a discussion of the points at issue ; but Fischer's whole 

 conception of the case showed such ludicrous ignoring of 

 demonstrated facts in bacteriological research and such retro- 

 grade notions of the general physiological aspects of microbial 

 infection, that some refutation was necessary. 



E. F. Smith, to whose investigations in this branch of plant 

 pathology we owe so much, took up the challenge and had no 

 difficulty in showing the completely erroneous nature of Fischer's 

 statements and " unwarranted assumptions." Smith has proved 

 that in the case of the Black Rot of the Cabbage fully ninety per 

 cent, of the infections take place through the water-pores, which 



