^12 Journal of Agricultural Research voi. xvni. No. lo 



F. discolor, var. sulphureum (Schlecht) App. and Wollenw. (Culture No. 203). Dr. 



WoUenweber's culture isolated at Dahlem, Berlin, in June, 1909. 

 F. eumartii Carp. (Culture No. 204). Isolated by C. W. Carpenter in January, 1914, 



from a stem-end dry-rotting tuber grown in Pennsylvania. 

 F. oxysporum Schlecht. (Culture No. 208). Isolated by H. A. Edson in October, 



1916, from potato tubers grown in New Jersey. 

 F. radicicola Wollenw. (Culture No. 211). Isolated by H. G. MacMillan in October, 



1916, from potato tubers grown in Colorado. 

 F. irickothecioides 'Wollenw . (Culture No. 214). Isolated by O. A. Pratt in October 



1916, from potato tubers grown in Idaho. 

 Verticillium albo-atrum Reinke and Berthold. (Culture No. 426). Isolated by C. W. 



Carpenter in September, 1915, from an eggplant grown at Shepherdstown, W. Va. 

 V. albo-atrum (Culture No. 427). Isolated by M. Shapovalov in September, 1917, 



from the vascular system of a wilted potato stem grown at Presque Isle, Me. 



The growth of these fungi at various temperatures was studied in 

 plates containing 10 cc. of a 2 per cent potato agar without sugar. A 

 small drop of a water spore suspension of the respective fungus was 

 placed in the center of each plate by means of a 2-mm. loop. The plates 

 were then distributed in the incubators running at from 1° to 40° C, with 

 approximately 5° difference between chambers. Additional sets of 

 plates of Fusarium oxysporum and F. radicicola were kept at 37° and 39°, 

 respectively, the maximum temperature here being of particular interest 

 on account of a thermophylic habit of these organisms. Observations 

 were made and measurements of the diameters of the colonies were 

 taken daily for a period of two weeks. At the end of the first week the 

 most rapidly growing colonies reached the edges of the plates; therefore 

 further data were of little comparative value and were omitted in the 

 final compilation. The tests were repeated three times in their entirety 

 and in some inconclusive cases four and five times. The average results 

 then were plotted and are presented in the accompanying graphs. 



DISCUSSION OF RESULTS 



A general examination of the figures i to 8, which represent daily accumu- 

 lations of growth, at once reveals a peculiar common feature in the 

 structure of the graphs: each series of curves characterizing the growth 

 of a given organism originates at scattered points to the left, the lowest 

 thermal points, then rises in the direction of the optimum temperature, 

 and finally falls to a single point at the right, the highest thermal limit. 

 Fusarium oxysporum and Verticillium albo-atrum No. 426 appear to be 

 slight exceptions to this rule, but only for the first day. Quite a con- 

 trasting picture is seen in figure 9, where each curve shows the amount 

 of growth produced by a corresponding organism for the total period of 

 7 days. Here, with but one exception, the entire series of curves has its 

 origin at a single point to the left and is distributed at different points to 

 the right. Thus, it is evident that the highest thermal point of growth 

 was reached within the first 24 to 48 hours, while the lowest limit did 

 not become apparent until the expiration of from 5 to 7 days. 



