. 224 



The words of Hiltner and Peters themselves best show how Httle the 

 organisms per sc are to be feared and how the chief cause of the disease is to 

 be sought in the conditions making the plants susceptible. In speaking of 

 the results of their experiments, they say (loc. cit. p. 249) "this result, how- 

 ever, shows that the production of diseased seedlings in the seed bed presents 

 a rather complicated phenomenon. This cannot be laid exclusively to the face 

 (heretofore almost universally accepted) that parasitic fungi or bacteria ac- 

 cumulate on the seed balls, then passing over to the roots, for these organ- 

 isms in themselves cannot cause the diseased conditions of the beet. Only 

 after the resistance of the roots has been weakened by the influence of cer- 

 tain substances, viz., oxalates, can otherwise harmless parasites attack them." 



According to Hiltner's theory, the substances or circumstances predis- 

 posing a plant to disease are produced by the decomposition of the tissue in 

 the seed balls, either on the field as a result of unfavorable weather, or later 

 in storage because of too great warmth. 



A work by Sigmund' reports upon the advance given to the occurrence 

 of rootblight by the fact that the micro-organisms especially concerned in 

 it (Phoma and Bacillus mycoides) find certain organic compounds in the 

 nutrient solution of the host. After he had emphasized the fact that the 

 parasites are not able alone to increase the disease, he mentions that the 

 number of diseased beet seedlings can be increased if glycocol, uric acid, 

 asparagin, hippuric acid, leucin, etc., are found in the nutrient solutions of the 

 micro-organisms named and the beet balls are soaked in this nutrient so- 

 lution. 



In this important disease we have simply listed, first of all, the various 

 theories and results of investigations as they have appeared from time to 

 time, in order to show that with all observers, in spite of their very different 

 points of view, one statement is found running through all their discussions 

 like a red line, viz., the influence of the soil'-. This influence shows itself 

 most distinctly in heavy, binding soils. It can make itself felt also on other 

 soils, if they are encrusted for any reason whatever. The prime factor under 

 such conditions is the scarcity of oxygen. At present we cannot say defi- 

 nitely what processes are started in the soil, seeds and the young plants. In 

 the same way, no definite decision can be made as to whether rootblight is a 

 constitutional disease, i. e. a deflection of the normal life functions leading 

 to tissue decomposition, or a parasitic process, i. e. a process producing the 

 same result but caused by the co-operation of micro-organisms. If, as \ye 

 believe, in the majority of cases the latter should be granted, we must bear 

 in mind emphatically the fact that these organisms, no matter whether fungi 



1 Sigmund, Wilh. Beitriige zur Kenntnis dcs Wurzelbrandes der Rube. Natur- 

 wissensch, Zoitschr. f. Land- und Forstwirtschaft, 190f>, ]). 212. 



- Further material from practical sources may be found in the annual reports 

 of the Special Committee for I'lant Protection. (Jahresberichte des Sonderaus- 

 schusses fur I'flanzenschutz. Deutsch. Landw.- Gesellscli. 1892-1905). 



