80 PROTECTION OF PLANTS — 1922-23 



The genus Fusarium possesses certain characteristics which make it spe- 

 cially adapted to a study of this nature. There are a large number of species, 

 (Saccardo hsts 401), and they are widely distributed in the soil. The spore types 

 are very characteristic and the genus possesses the power of chromogenesis to 

 a marked degree. The genus also exhibits a wide variation in characters when 

 grown en artificial media. In addition to these factors, a great deal of work has 

 been done in recent years on the taxonomy and pathogenicity of the genus 

 Above all, the Fusaria appear to be becoming of increasing importance as pro- 

 ducers of disease in economic crops. 



Scope of work. 



The investigations have been carried out under three main heads: — 



1. The determination of a number of species of Fusarium isolated from 

 various sources; 



2. The study of their growth on various media; 



3. The study of their growth at different concentrations of the hydrogen- 

 ions in the media. 



In determining the species the literature chiefly relied upon has been the 

 classic monograph of Appel and Wollenweber (1: 1910), subsequent articles 

 by Wollenweber (16: 1913), Sherbakoff's work on the potato Fusaria (12: 1915), 

 and subsequent articles, based on these, by other investigators. Exact identi- 

 fication was not found possible in every case and in such an instance the species 

 with which the organism most closely agrees is given. The growth character- 

 istics of the various organisms isolated have been studied on as wide a range 

 of media as possible, and observations made on the effect of tempareture. 

 Detailed descriptions of the macroscopic and microscopic characters were made 

 and from these observations certain tentative conclusions have been drawn. 

 In order to secure data in regard to the effect of various concentrations of the 

 hydrogen-ions in the media, a series of cultures were grown on media standard- 

 ized to diffeient Ph values. The colorimetric method of Ph determination des 

 cribed by Clarke and Lubs (5: 1917) and more fully by Clarke (4: 1921) was 

 used. 



Culture media. 



In all, seventeen different media were utilized and they may be grouped 

 under two main heads, namely, natural and synthetic. The first group consists 

 chiefly of plant media, either in the form of steamed plugs or combined with 

 agar. In the second group are a number of well known nutrient solutions, both 

 in the liquid form and combined with agar. The media used are as follows : 



