Pethybridge — On the Rotting of Potato Tubers. 533 



the Temporary Station for the Investigation of Plant Diseases, established by 

 the Department of Agriculture and Technical Instruction for Ireland, at 

 Clifdeu, Co. Q-alway, and has since been received from other parts of the 

 country. Owing to the prior claims of work on other diseases, and to the 

 fact that this new one was for the. first two seasons not particularly prevalent 

 in the plots at Clifden, the detailed study of it was postponed for a time. 

 During the last two seasons, however, the disease has become of increasing 

 virulence, particularly on certain portions of the land which, for special 

 reasons, have been cropped continuously with potatoes ; and it has been found 

 to be prevalent in many of the fields of the small farmers in the surrounding 

 district, where it causes considerable loss. 



A preliminary note on the disease, under the title " Doubtful " rot, was 

 published (20) early in 1912, when the cause of the rot had |not been fully 

 worked out. Since then tliis lias been done ; and a study of the fungus 

 which causes it has I'evealed a mode of development of the sexual oi-gans of 

 hitherto unsuspected occurrence amongst the fungi, but which has been found 

 to be common also to Phijtophthora infestans, P. Phaseoli, and probably to 

 some other species of the same genus, while it does not occur in the case of 

 others, such as P. Fagi, P. Syringae, and P. Cadonun. 



For this new fungus the name of Phytophthora erythroseptica is proposed ; 

 while for the disease caused by it in the tubers the trivial name of " Pink 

 Eot " may be suggested. 



II. Description of the Eot. 



Although it is quite possible (and certain preliminary observations and 

 experiments seem to point to the probability) that the disease to be described 

 attacks parts of the potato plant other than the tubers, yet since it is almost 

 entirely to the rotting of these that attention has been devoted up to the 

 present, this phase of the subject alone will be considered here. 



The rot commences when the tubers are still in the ground ; but at what 

 particular period the infection first occurs has not been ascertained. It, is to 

 be found, however, well developed in the tubers of early varieties dug early in 

 July ; and, speaking generally, it is rather tlie larger and older tubers which 

 are found to be attacked at the time of digging the crop than the smaller and 

 younger ones. 



In the great majority of cases the rot begins at the proximal or 

 " heel " end of the tuber, and progresses rather quickly towards the distal or 

 " rose " end. In only two cases out of very many hundreds of tubers which 

 have been examined has the rot been found to start at a point other than 

 at the heel-end, viz., at the side of the tuber ; and in one of these cases it had 

 evidently started from a wound in the skin at this point. 



