H. WORMALD on 



one was found on the ground on September 29, and two others, which 

 were discoloured over the whole surface with the exception of a small 

 green patch near the eye end, fell at a touch on the same day; the other 

 two hung on the tree until October 15, by which time they were soft 

 and discoloured over the whole surface, the stalks being brown and 

 withered. Again no reproductive bodies were to be found on these pears 

 while they remained in the greenhouse, but on being transferred to a 

 damp chamber sporangia readily appeared within a few days. 



About six weeks after the inoculations were made one of the pears 

 was cut across and examined for the presence of mycelium in the tissues. 

 Non-septate hyphae were found extending to the centre of the pear, 

 invadino; the cavities of the core and forming a coverino; round the seeds ; 

 strands of mycelium were seen even within the seeds themselves. A 

 small portion of the testa with the adhering mycelium was removed 

 from one seed and after washing in several changes of sterilized distilled 

 water it was transferred to agar in a test tube; a typical pure culture 

 of the Phi/tophthora resulted, sexual organs developing within five days. 



Inoculation Experiment 6. From one of the pears used in the last 

 experiment sporangia were transferred to a little distilled water on a 

 glass slide; after a few hours numerous zoospores were set free so drops 

 containing motile zoospores were placed on the stalk end of two pears 

 on a tree in the greenhouse on September 29, while the pears were still 

 quite hard and not nearly ripe. One of the pears was found detached 

 on October 2 although no signs of rot were evident. The second fell 

 on October 9 and showed a discoloration extending from the stalk 

 end for about 1 cm. down one side; the pear was placed in a damp 

 chamber and within three days the rot had extended all round the stalk 

 end to a distance of from 1-3 to 2-2 cm. and sporangia were present. 



As the atmosphere in the greenhouse was rather dry the inoculations 

 were made in the evening and the two pears were enclosed in transparent 

 water-proof bags containing a little absorbent cotton wool soaked with 

 distilled water; these precautions were adopted to prevent the rapid 

 evaporation of the drops of water containing the zoospores. 



The result suggests that the zoospores are able in certain circum- 

 stances to cause infection through the uninjured skin, particularly in 

 a moist atmosphere. On repeating the experiment the following year 

 on eleven pears, not enclosed in bags, negative results were obtained in 

 all cases. 



The Sporangia and their Mode of Germination. As found on the 

 affected pears the sporangia were mostly elliptical or citriform ; the 



