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



187 



The flasks of this medium were inoculated and the fungi allowed to grow 

 for two or three weeks. The mat of mycelium was then removed, washed, 

 dried, ground, and analyzed. The data obtained from these analyses, 

 calculated as percentage of the dry weight, are given in Table VII. 



Table VII. — Amount of akohol-insoluble substance reducing Fehling's solution when 

 hydrolyzed with dilute hydrochloric acid, pentosans, methyl pentosans, galactans, and 

 crude fiber in mycelium of Fusarium oxysporum and Fusarium radicicola 



[Expressed as percentage of dry weight] 



It is apparent from Table VII that the fungi growing on the culture 

 media prepared from potatoes produce pentosans, methyl pentosans, 

 galactans, and a considerable quantity of substance which is insoluble 

 in alcohol and reduces Fehling's solution when hydrolyzed with dilute 

 hydrochloric acid. That this last-mentioned substance can not result 

 from the hydrolysis of the pentosans is evident from the relatively small 

 pentosan content of the mycelium. The amount of substance which is 

 considered as crude fiber in the table is also quite marked. It is evident, 

 then, that both fungi build compounds which may be expected to raise 

 the content of pentosans, galactans, and other substances in the tissue 

 of the potato when the fungi and host are analyzed together. It must 

 be remembered, however, that the percentages given in Table VII are 

 related to dry weight of washed fungus mycelium and that the content 

 of mycelium in 25 gm. of wet weight of the potato rotted with either of 

 these fungi would be small. 



The general appearance of the rotted portion of potato was typical 

 for tubers rotted with these fungi at laboratory temperatures (from 20° 

 to 25° C.) in a saturated atmosphere — that is, it was a wetrot (4, p. 187). 

 The skin apparently was uninjured and could have been removed entire 

 in most cases. The inner portion was soft and generally disorganized. 

 Microscopic examination showed that the cells of the interior were appar- 

 ently free from each other, as if the middle lamellae had been dissolved. 

 The starch grains did not appear to have been eroded in the time allowed 

 for the experiment. The method of preparing the quarters of potato 

 for analysis has been described. 



The starch and sugar determinations were usually made on the same 

 portion by extracting the pulp with alcohol, the extract being used for 



