[ 179 J 



X. 



FUETHER OBSERVATIONS ON PHTTOPHTEORA ERYTHRO- 

 8EPTICA PETHTB., AND ON THE DISEASE PRODUCED 

 BY IT IN THE POTATO PLANT. 



By GEORGE H. PETHYBRIDGE, Ph.D., B.Sc, 



Economic Botanist to the Department of Agricultuie and Technical 

 Instruction for Ireland. 



(Plate XIII.) 



[Read Dbceiieer 16, 1913. Published January 31, 1914.] 



In a communication! brought before the Society early in the present year 

 and published in March last, a description of a new form of rot in the potato 

 tuber, caused by a new species of Phytophthora, was given. 



Apart from the nature of the rot and the very considerable losses 

 occasioned by it in certain parts of the country, the organism causing it 

 (to which the name Phytophthora erythroseptica was given) is of peculiar 

 interest, inasmuch as its sexual organs are developed in a manner which, at 

 the time of publication of the paper referred to, was wholly novel and 

 unprecedented. 



Shortly stated, the course of events is as follows : — The oogonia and 

 antheridia are borne on separate hyphae ; the oogonial incept, at a very early 

 stage, penetrates into the interior of the previously developed antheridium at 

 or near its base, grows up through the latter, breaks out at its summit, and 

 expands rapidly to form that portion of the oogonium in which shortly after- 

 wards first an oosphere, and then a thick-walled oospore, develops. Whether 

 fertilization actually occurs is not yet known ; but, if it does, it probably takes 

 place before the oogonial incept emerges from the antheridium and before 

 the formation of the oosphere. 



Cultural studies of several other members of the genus Phytophthora, 

 wiiich are described in the paper referred to, and, as regards P. infestans in 



> Pethybridge, G. H. : " On the Eottingof Potato Tubers by anew species of Phytophthora, 

 having a method of sexual reproduction hitherto undescribed." Sci. Proc. Roy. Dublin Soc, vol. xiii 

 (N.S.). No. 35, March, 1913. 



SCIKNT. PEOC. K.D.S., VOL. XIV., NO. X. 2 E 



MAY 18 1914 



