REPORT OF THE SOCIETI 



83 



further studies and named the causal organism Synchytrium endohioiicum. 

 Its appearance on this side of the Atlantic was first announced by Gussow 

 in 1909 from Newfoundland material. 



Symptoms 



On above-ground parts there are rarely any sj^mptoms but occasionally the 

 fungus may gain entrance to the haulm, lower axillary buds or leaves. If this 

 happens the infected tissue is stimulated to excessive growth giving rise to 

 variously shaped excrescences. It is on the tubers that the symptoms are 

 usually found and here the buds or eyes are affected. Diseased buds are sti- 

 mulated to such hypertrophic growth that they may be no longer recognisable. 



If the eye is affected late in the 

 season of its growth, the nodular 

 excrescences may be noticeable only 

 on careful examination. But if the 

 eyes are attacked while the tuber 

 is quite 3'oung the excessive growth 

 of the tissues will give rise to nodul- 

 ar masses entirely unlike a tuber. 

 (See Fig. 10). The demand for 

 food on the part of the organism 

 will be so great that any stored in 

 the developing tuber will be used 

 and the tissues will collapse. In this 

 necrotic condition lies the greatest 

 danger. It is impossible to harvest 

 such diseased tubers without leaving 

 behind fragments, which are filled 

 with sporangia, in the soil. The 

 resting sporangia thus lett behind 

 may remain viable for several j'ears 

 and constitute a source of infection 

 if potatoes of a susceptible variety 

 are planted. Cases are on record 

 in which the disease has reappeared 

 after an interval of ten years in 

 England. 



Life History of the Fungus 



Fig. 8— Potato Caxker — Imoeptible varie- rj^x ^- • i- i 



ty (Cumberland Ideal) showing effect on tubers. The restmg sporangia whlch ave- 



Two cankers on above-ground parts can be seen, rage about 52 microns in diameter 

 (From 8upi)lement IS to Jour. Bd. Agric. Eng. 

 1919.) 



contain many round zoospores which 



