W. MCRAE 239 



fairly luxuriant. On Quaker-oats-agar tlie growth progressed as fast as that 

 in French-bean-agar, but was more dense. On maize-agar and cowpea-agar 

 the growth was very good extending to 2 centimetres on the second, 6 centi- 

 metres on the ninth, covering the whole surface by the fourteenth day, and 

 filling up the space between the agar and the other side of the tube. The 

 mycelium was dense, white, and flocciilent. The luxuriance of growth of 

 the mycelium in the culture media increases according to the order in which 

 they have been described. On carrot and potato slabs hyphse appeared on the 

 second day and gradually spread all over the surface by the fourteenth day, 

 becoming more dense by the end of a month. Sporangia appeared in the 

 tubes from the third to the eighth day except in the agar-agar and glucose-agar 

 tubes where they were present between the seventeenth and twenty-ninth days 

 and in the potato-agar and Hevea-a,gax tubes where they were not present after 

 two months. The main difference lay in the fact that in some media the gro^^i,h 

 was almost entirely submerged, in others though at first submerged was later 

 scantily aerial, and in others aerial and copious from the first and also in the 

 varying intervals at which sporangia were produced. Though examined a 

 year afterwards, none of the tubes contained oogonia. 



Inoculation experiments. 



The plants used for inoculation at Coimbatore were all grown in the 

 plant-house from seed and were from one to two years old. It was found 

 impossible to establish stumps as the young trees could not withstand the 

 dry winds in the hot weather even when protected, as much as possible by 

 other plants. In Kallar at the foot of the Nilgiris a small Govermnent 

 garden of Hevea trees up to 13 years old was at my disposal, and here 

 neither fruit-rot nor leaf-fall occur and Phjtophtliora has not been found. 

 The plants used for experiment were thus never exposed to infection from 

 Phytophthora before being used. The infective material used was taken from 

 pure cultures in French-bean-agar and consisted of minute pieces of mycelium 

 wth mature sporangia actively discharging zoospores in sterile distilled water 

 or of the water containing zoospores just discharged. 



(1) On leaflets of the plant. The leaflet was bent slightly and held in 

 position by a split stick or a piece of thread in order that the drop of water 

 might remain in one place, or two adjacent leaflets were held together hghtly 

 and the drop of water placed between them. The plants when small were 

 placed under large bell-jars or in glass cages and the leaf was placed in an 

 Erlenmeyer flask suitably supported when a large plant was used. 



