May 1. 1916 Effect of FusaYium spp. on Potato Tubers 



189 



The starch determinations in the sound and rotted portions of the 

 same tuber were made by two methods, as has been said. The data 

 obtained by the direct acid hydrolysis method are given in Table IX, 

 while the results of the determinations by the diastase method with sub- 

 sequent acid hydrolysis are shown in Table X. 



Table IX. — Starch content of sound and rotted quarters of potatoes infected with different 

 species of Fusarium, as found by direct acid hydrolysis 



[Expressed as percentage of starch of the original wet weight] 



Table X. — Starch content of sound and rotted quarters of potatoes infected with different 

 species of Fusarium asdetermined bythediastase method with subsequent acid hydrolysis 



[Expressed as percentage of starch, wet weight] 



Potato No. 



25 

 33 

 27 



Fusarium oxysporum. 



Rotted 

 quarter. 



17.77 

 12. 50 

 15-32 



Sound 

 quarter. 



16.85 

 II. 32 

 14.05 



Potato No. 



47- 



Fusarium. radicicola. 



Rotted 

 quarter. 



17-50 

 16.66 



Sound 

 quarter. 



16.66 

 15. 16 



The effect of the fungi upon the starch in the potatoes is in marked 

 contrast to their action on the sugars. In Table IX, which gives the 

 results of starch determinations by the direct acid-hydrolysis method, it 

 may be seen that the starch content of the rotted portion appears to 

 be higher in many cases than that of the corresponding sound quarter. 

 In the determinations by the diastase method followed by acid hydrolysis 

 the apparent starch content of the rotted portion is always higher, as 

 shown in Table X. The fact that the fungi build up substances which 

 are insoluble in alcohol and reduce Fehling's solution when hydrolyzed 

 with dilute hydrochloric aicd, as shown in Table VIII, would account 

 for any apparent increase in starch content in the rotted portion when 

 the starch is determined by the direct acid-hydrolysis method. If the 

 substances are also either soluble in hot water originally or made so by 

 the diastase treatment, the apparent increase in starch content when 

 the starch is determined by this method would be explained. In the 

 diastase method the starch paste is liquefied by the action of the diastase, 



