00 A PJn/tojyhthora Rot of Pears and Apples 



recorded by Bubak(i) as occurring in Bohemia: from his descriptions 

 and figures there is reason for assuming that the disease he observed is 

 identical with that of the Hertfordshire specimens. The clusters of 

 sporangia, which he observed on the pears, he refers to as "stark 

 lichtbrechen Kornchen, die habituell kleinen Zuckerkristallen ahnlich 

 waren." About the same time Unamuno(i2) found Phytophthora Cac- 

 torum associated with a disease of pears and cherries in 8pain. In 1912 

 Osterwalder(5, (!) again refers to the occurrence of this fungus oji apple 

 trees in Switzerland, a die-back of the shoots being observed in this case. 



While the outbreaks mentioned in the present article were under 

 investigation two other references to fruit rots caused by a Phi/lophthora 

 have appeared. Schoevers(ii) in 1915 recorded a rot of pears in Holland 

 attributed to P. omnivora, and in 1916 Whetzel and Eosenbaum(i3) 

 mention a Phytojihlhora rot of apples as occurring in America. The latter 

 isolated P. Cactorum from the diseased fruit and were able to reproduce 

 the disease on apples on the tree by inoculations with mycelium from 

 pure cultures. 



As the disease appeared to be of some economic interest and one on 

 which no work had been done in this country more specimens were 

 obtained, and these showed the same general features as those previously 

 examined. The letter accompanying them stated that "the smaller 

 variety is Foiidante d'Automne, the larger one Doyenne du Comice; 

 all the pears of the former one started to go at the base and fell within 

 three days, now the latter pear has just commenced to fall in exactly 

 the same way." 



On keeping the affected pears in a closed glass vessel the sporangia 

 were gradually replaced by sexual organs and oospores, the latter 

 22-30 /x in diameter, with smooth walls; the sexual organs were of the 

 Phytophthora Cactorum. type or genus Nozemia of Pethy bridge (7). It was 

 highly probable therefore that the sporangia and the oospores belonged 

 to one and the same organism and inoculation and cultural experiments 

 confirmed this supposition. 



Inoculation Experiment 1. Three pears were wounded by making 

 cuts through the skin, and sporangia from an infected pear were placed 

 on the wounds; at the end of 20 days one of the pears had produced 

 sporangia while on the other two only sexual organs were found. A pear 

 which had been inoculated at the same time by placing sporangia in a 

 drop of water in the hollow at the stalk end, without injury, showed no 

 change after 20 days. 



The fungus was then grown in pure cultures. No difficulty was 



