240 phytophThora meadii n. sp. on hevea brasilieksis 



The first sign of discoloration was noticed on the 3rd or 4th day after 

 inoculation. The discoloured area became pale, flaccid, and wrinkled, and 

 extended till it involved the whole leaflet which became slightly twisted. 

 Infection took place both from the lower and the upper smface. When the 

 air was very moist hyphae and sporangia were fomid copiously on the surface, 

 but when air was allowed access to the jars so that the air in the jars was fairly 

 dry, few hyphae were found on the surface. "When an infected leaflet was made 

 to touch another that other became infected, and when drops of water were 

 allowed to pass from a leaflet that had ripe sporangia the leaflets on which the 

 drops fefl became infected. Infected leaflets feU from the 9th to the 16th day 

 after inoculation. In some cases an infected leaflet fell and the plant remained 

 healthy. When the discoloration passed down the petiole the other leaflets 

 also fell and sometimes also the petiole but it sometimes remained on the stem 

 for several days — sufiiciently long to allow of other natural factors coming into 

 play to cause its fall. In section the germ- tubes of three zoospores were seen 

 passing through the cells of the upper epidermis into the paUsade parenchyma 

 and the germ-tubes of two passing into a stoma on the under surface. The 

 appearance of the leaf -spot in section was hke that in nature, and the characters 

 and measurements of the hypha3 and sporangia of the fungus within the leaflets 

 agreed with those of the Phytop/dhom in culture. Re-cultures made from sporangia 

 from these leaves were used subsequently with success to infect fruits. 



(2) On the leaf -by ds. On young bursting leaf -buds discoloration appeared 

 on the 3rd to the 5th day ; the small pale leaves became flaccid and collapsed 

 or fell off and the bud shrank. Copious mycelimn and sporangia were usually 

 produced. In a few cases the bud dried up and fell ofl leaving the plant healthy 

 for some weeks, and sections at the place of abscission failed to show the 

 presence of hypha^. In other cases the discoloration gradually passed down 

 the stem or the branch, each leaf falling off in succession. When dry air 

 conditions were induced the progress of the discoloration stopped, but when 

 the plant was kept in moist-air conditions all the time the discoloration 

 continued till the plant was killed. The control plants remained healthy 

 throughout. After an artificial infection of a bud and the subsequent dying- 

 back of the branch the Phytophthora has not yet been observed to begin again 

 in the new season, but this negative result is due to accident and insutticient 

 work on this point of the subject. From a naturally infected bud, however, 

 this has been traced as noted on page 236. 



(3) On the petiole. The leaflets were pushed through a glass tube so that 

 it surrounded the petiole. The ends were plugged loosely with cotton-wool 

 and the tube suitably supported so that there was no strain on the petiole. 



