194 



Journal of Agricultural Research 



Vol. VI. No. s 



bination in which they occur in the tuber was not investigated. Galactose 

 might occur in combination with raffinose, in a glucoside or combined in 

 the cell walls. It probably occurs in plants most commonly in the last- 

 mentioned combination. The effect of the fungi upon the galactan con- 

 tent of the potato is shown in Table XVI. 



Table XVI. — Galactan content of sound and rotted quarters of potatoes 

 [Expressed as percentage of wet weight] 



Rotted with Fusarium radicicola. 



Rotted with Fusarium oxysporum. 



Potato No, 



Rotted 

 quarter. 



Sound 

 quarter. 



Potato No. 



Rotted 

 quarter. 



Sound 

 quarter. 



27 

 42 



0.039 



•033 

 . 029 



o. 062 



. 060 

 .030 



166 

 167 



172 



o. 069 



.068 

 .081 



o. 071 



. 076 



.083 



It is evident from the table that the fungi lower the galactan content 

 of the potato. The fungi produce galactans when growing upon potato 

 extract and the data in Table XVI show that the breaking down process 

 proceeded faster than the building up. 



The amount of dry matter of the sound and rotted quarters determined 

 as mentioned earlier in this paper is shown in Table XVII. 



Table XVII. — Amount of dry matter in sound and rotted quarters of potatoes 

 [Expressed as percentage of wet weight] 



Rotted with Fusarium radicicola. 



Rotted with Fusarium oxysporum. 



Potato No. 



27 

 42 



Rotted 

 quarter. 



20. 83 

 19.88 

 20. q8 



Sound 

 quarter. 



21. 19 



22. 59 

 22. 13 



166 

 167 



Rotted 

 quarter. 



17-73 

 18.93 

 18. 17 



Sound 

 quarter. 



18.91 

 20.45 

 19.36 



As was to be expected, the rotting of the potato by the fungi lowered the 

 percentage of dry weight as calculated to the original weight of the portion 

 of the potato used in the experiment. This is probably due to an increased 

 respiration — that is, a respiration of the quarter of the potato plus the 

 respiration of the fungus which in a given time is greater than a portion 

 of the same potato alone. 



DISCUSSION 



From the foregoing pages it is evident that the tuber-rot fungi used 

 in this study considerably alter the composition of the potato. That 

 they should be able to utilize the sugars of the potato was to be expected. 

 Most fungi use glucose readily as a source of carbon. Behrens (i) has 

 shown that Sclerotinia fructigenia lowers the sugar content of apples in 



