218 



PHYTOPHTHORA SP. ON HEVEA BRASILIENSIS 



cell cavity is sometimes filled with a yellow or brown gummy substance. On 

 account of the death of the protoplasm and the loss of the water contents of 

 the cell the cell walls collapse. The depression of the diseased area may be 

 due to this collapse of the cell walls of the outer tissues. It is between 

 these swollen and diseased cell walls that unseptate hyphsB are to 

 be found. 



It is difficult to trace the hyphse, as they are generally completely masked 

 bv the presence of the brown pigment, which also prevents the affected cell 

 walls from being stained by staining reagents. The presence of the hyphae 

 can be detected when the sections are treated with dilute ammonia or when 

 thev are subjected to ammonia vapour for a minute ; chloral hydrate also 

 tends to cleai the pigment and thereby to reveal the presence of the fungus ; 

 boiling the sections for a few seconds in hydrochloric acid, as recommended by 

 Ducomet,^ either completely removes the pigment or leaves in the tissues 

 only a slightly yellow tinge, if then washed in water and boiled with lactic 

 acid, the hyphse can be seen and will stain faintly blue with cotton blue. The 

 hyphse in the stem have been found to be intercellular and confined to the soft 

 tissues. They are not to be found between the walls of the sclerotic cells 

 though the latter are often filled with the blown gummy substance ; they 

 are also absent from between the walls of the wood cells. Haustoria are 

 of rare occurrence and have been chiefly observed in the cortex ; they are 

 globose or finger-shaped (Fig. 1). In the tissues of the rind of the diseased 



fruits the mycelium is both 

 .1, ^>§5=^ inter-and intra-cellular. The 



'i!^ • (^^ hyphse are confined to the 



tissues of the rind. They 

 have not been found to 

 penetrate the tissues of the 

 woody shell, but in ad- 

 vanced cases of attack they 

 reach the inside of the 

 shell through the sutures. 



Fig. 1. Intercellular mycelium with haustoria from Bacteria and fungi like 



diseased tissiipfl of the stem. x365. 7^ . ?• 7 7- -n 



Fig. 2. Germination of the zoospores. X 481). Botnjodlplodia, iusanum, 



Nectria, Gloeos'jwrium and 

 others coming in the wake of Phytophthora then completely destroy the fruit. 



' Ducomet, V. Reclierches sur le d6veloppement de quelques champignons parasites h 

 thalle suhcuticulaire, p. 11, 1907, 



