200 Pflanzenkrankheiten. 



of burs, showed mycelium at their bases, indicating ihat they had 

 become infected in the burs and had afterward dropped out. 



____ M. J. Sirks (Haarlem). 



Smith, R. E., The investigation of „physiological" plant 

 diseases. (Phytopathology. V. p. 83 — 93. 1915.) 



In conclusion the writer summarizes his ideas on this subject 

 as follows: 



There is no such thing as an established group of physiological 

 or non-parasitic plant diseases for the kind ol troubles which we 

 have been considering. There is among them not even a Single, 

 well proven example. They are all more or less obscure diseases 

 of unknown etiology, which, for one reason or another, have not 

 yet been accounted for. 



In all diseases found to be really infectious, either through 

 inoculation with plant parts or juice, by budding or grafting or by 

 any transmission method producing true infection in normal plants, 

 it is best to assume a parasitic factor. 



The only positively known inciting factors in plant disease 

 (excluding direct traumatisms) are parasites. In the investigation of 

 diseases wherein an obscure, ever active, inciting factor appear? to 

 be present, we should there fore proceed from the known to the 

 unknown, endeavoring within reasonable limits to exhaust every 

 known phase of parasitism before assuming conceptions of no esta- 

 blished importance. 



Nothing is more important than a thorough knowledge of the 

 pathological histology and cytology in these diseases, although such 

 knowledge is at present extremely lacking. 



Biochemical work is likewise of great impartance, but may 

 easily be so superficial as to result in false and misleading con- 

 clusions. 



The study of these diseases should include every part of the 

 plant and not simply those where gross s3'mptoms or lesions appear. 



The most substantial proof should be obtained before final con- 

 clusions are drawn. Tentative or incomplete results may be worth 

 Publishing but should be clearly stated as such, with the attendant 

 methods and circumstances, giving the reader an opportunity of 

 drawing conclusions of his own. Many facts but few conclusions is 

 a safe rule in such cases. 



A thorough knowledge of pathological histology and chemistrj^ 

 of diseases of known cause is equally important, espectally for the 

 elucidation of obscure troubles by comparison. 



The greatest progress in fundamental know^ledge of plant disease 

 can be made only by pathologists; not mycologists, physiologists, 

 bacteriologists, cytologists, or chemists, but men who combine an 

 intelligent interest in and appreciation of these Clements in their 

 relation to the study of disease. M. J. Sirks (Haarlem). 



Smith, R. E. and A. Boncquet. New light on curly top of 

 the sugar beet. (Phytopathology. V. p. 103—107. 1915.) 



The evidence of Ball (1909) and Shaw (1910) as to this peculiar 

 disease being incited b\^ the sting of the minute leaf hopper, Eiiteft/x 

 tenella Baker, has never been fuUy accepted bj' entomologists and 

 pathologists, owing to the unique importance of the fact and various 



