232 PHYTOPHTHORA MEADII n. Sp. ON HEVEA BRASILIENSIS 



lacuna of the cortex, the mycelium was richly developed. Hyphfie were not 

 found in the branch beyond 1 centimetre from the point of insertion of 

 the fruit-stalk. When a leaf-bud is infected, the hyphae pass inwards from 

 the young infected leaves, kill the growing point, and continue downwards 

 into the young branch. They pass more quickly along the branch in this 

 case than they do from a fruit-stalk, possibly because the tissues behind the 

 growing point of a leaf-branch are more succulent and less differentiated 

 than, and the cell-contents have a different reaction from, those from which 

 the fruit-stalks arise. Green branches may become directly infected by 

 hyphao that penetrate their epidermis. Occasionally a young green branch 

 has been found with a single isolated discoloured patch on an internode, and 

 eections have shown the presence of the Phyfophthora. 



During the dry weather the fungus is not active anywhere on the outside 

 of the tree. Experimental work with it on the tree in the field during that 

 period was brought to a stand-still ; it was found impossible by ordinary means 

 to infect leaves or branches, and only when they were placed under bell-jars 

 in moist chambers was it possible to continue. The only two places where 

 the living fungus has been found at this season are as mycelium near the 

 junction of dead and living tissues in a branch that had partially died back, 

 and at the insertion of the stalk of a fruit that had been infected during the 

 previous monsoon, and it no doubt also exists as oospores in the dried up fruits. 

 From these places it can begin its activity in the new season when the early 

 rains come, and conditions are sufficiently moist to enable it to develop. 

 The geirmination of oospores has not yet been observed ; they have been found 

 in nature on the fruits alone, and that but seldom and in small numbers. The 

 development of the fungus from a small crack at the point of insertion of an 

 old fruit-stalk was observed in April. Non-septate hyphse from 4 to 5/a in 

 diameter were present in the fruit-stalk and in the branch below the point of 

 insertion as far as the pith. They had grown into a small depression on the 

 exterior, and formed sporangia measuring 32'4 — 5r2xl9"2 — 2Q'8ix (only 

 6 were measured), some of which discharged their zoospores "when kept in 

 water on a glass-slide. There was no appearance of the fungus on any other 

 part of this twig, nor on those immediately surrounding it ; the leaves were not 

 affected, and the flowers and very young fruits were healthy. There seemed 

 no possibiUty of outside infection at that time, nor immediately before. It is 

 reasonable to suppose that the mycelium that had entered the fruit-stalk and 

 the branch from the previous year's infection, had remained alive within the 

 branch and was developing in the moist conditions when the rain came. 



