26 Journal of Agricultural Research vol. xx. No. i 



the condition desirable for successful infection. Since the glassine bags 

 were transparent, the heads were not seriously deprived of sunlight. 

 When the weather was very dry and warm the bags had to be opened 

 and the cotton again moistened to saturation. All controls were treated 

 in the same way as inoculated plants, except that they were sprayed 

 with water to which no spores had been added. 



Since Gibberella saubinetii usually produces very few conidia in culture, 

 and since large quantities of spores were required for inoculations, it was 

 necessary to contaminate the cultures purposely with a certain bacterium 

 which has been found to bring about a great increase in sporulation. In this 

 way large quantities of spores could always be obtained. The bacterium 

 has not been identified, and the nature of its effect upon cultures of G. 

 saubinetii is not known. Further study of this relationship is planned 

 for the future. 



The employment of such conidia for inoculation naturally raises the 

 question whether the bacterium present has some effect on the patho- 

 genicity of Gibberella saubinetii or whether it itself is pathogenic on 

 wheat. In order to establish this, numerous wheat heads were inocu- 

 lated at the same time with pure G. saubinetii conidia and others 

 with a suspension of a pure culture of the unidentified bacterium. In 

 all cases the heads inoculated with G. saubinetii conidia became blighted, 

 while all heads inoculated with the bacterium suspension remained per- 

 fectly free from blighting or other injury. This shows that the bacte- 

 rium favoring the sporulation and perithecia formation of G. saubinetii, 

 as mentioned before, is not pathogenic on the wheat heads and has no 

 effect upon the pathogenicity of G. saubinetii. 



Wheat, spelt, rye, barley, and oat heads, as well as heads of Agropyron 

 repens when inoculated with a conidial suspension or an ascospore sus- 

 pension of Gibberella saubinetii became blighted. The blighting of A. 

 repens proceeded exactly as observed in nature. In over ioo inoculation 

 experiments in which over 3,000 heads of the various cereals, mostly 

 wheat heads, were concerned, some infections always resulted. The 

 number of blighted heads in each experiment varied from over 50 per 

 cent to 100 per cent. In the majority of the experiments, all inoculated 

 heads became infected and typically blighted. On many of these heads 

 conidia were formed, and on some even the perithecia of G. saubinetii 

 developed before the harvesting of the plants. 



The inoculation experiments gave positive results from the time of 

 blossoming till the latter part of the dough stage. Inoculation made 

 before the first and after the second stage gave either negative or very 

 doubtful results. 



PERIOD OF INCUBATION 



On seedlings. — The period which elapses between the inoculation 

 and the time the first symptoms of attack on the seedling roots appear 

 varies so much that no definite incubation period can be given. It varies 



