22 Journal of Agricultural Research vol. xx.No. r 



In order to prove that the Fusarium conidia produced on a blighted 

 wheat head are the conidia of the causal organism and not of a secondary 

 organism which has followed the first, parts of a large number of blighted 

 wheat heads were washed in distilled water to moisten them and then 

 disinfected by dipping them in i to 1,000 mercuric chlorid solution 

 (HgCl 2 ) for two minutes. After this they were rinsed in distilled water 

 and then transferred with a sterile needle to cooled poured plates of a 

 suitable medium. In all cases only one organism was isolated from each 

 blighted head, and this was in all cases the same as the one obtained from 

 the conidia on this head. This is so true of the Fusarium organisms 

 causing headblight that the causal organism upon a clean, undiscolored 

 Fusarium-blighted head may almost surely, and even without micro- 

 scopic examination, be described as one and pure. In rare cases the 

 blighted heads may also be smutted, rusted, or brown spotted and dis- 

 colored; and in such cases, of course, more than one organism may be 

 found on a head. Such heads were discarded and never used for study 

 or isolation. 



Plain water agar ' was used for diluting the conidia and for pouring 

 the plates. After 12 to 24 hours the plates were examined micro- 

 scopically, and single, germinating conidia were marked on the plate; 

 then with a sterile needle made for the purpose they were transferred to 

 test tubes containing suitable medium, usually hard oatmeal agar. In 

 all cases five single, germinating conidia were transferred, with only one 

 to each test tube. This was done to make sure that there was not more 

 than one species of Fusarium present. Except in rare cases when some 

 of the test tubes were contaminated during the manipulation with for- 

 eign organisms such as Penicillium or bacteria, all five test tubes yielded 

 the same species. To make certain, however, that the cultures were 

 free from bacteria they were transferred to plates, and second transfers 

 were made from the margins of the plate colonies. The pure cultures so 

 obtained were used as stock cultures for further study. 



Inoculation work. — In this paper only the results of inoculation 

 with Gibberella saubinetii are given. The writer was able to produce 

 blighting of heads of wheat and rye by inoculation with several of the 

 species mentioned above and was able to produce more or less severe 

 seedling-blight by inoculation with nearly all of them, but the condi- 

 tions under which these species become pathogenic are not yet well 

 understood. 



Seed and soil inoculation. — A number of methods have been used 

 in artificially infesting soil with species of Fusarium. Most of them 

 consist in growing the particular organism on a suitable medium and 

 then introducing the whole culture into sterilized soil. Such a method 

 is very good, except that it is an artificial one which does not reproduce 



1 One liter of distilled water and 25 gm. of bacto-agar. 



