DISEASES OF COCONUT 187 



from withering of the leaf-blade caused by Thielaviopsis. The 

 young leaves next in order are successively attacked and the 

 central column falls out leaving the ring of outer green leaves. 

 At the seat of the disease brown sunken spots up to 3 inches in 

 diameter are found existing on the leaf bases and penetrating 

 them successively until the apex of the stem is reached. At 

 the stage of the withering of the heart leaf the heart itself is 

 usually already soft-rotted. 



The Causative Fungus. 



The tissues of the leaf-base spots and of the stem apices when 

 these are not already soft-rotted are penetrated by a stout, 

 sparingly septate, intercellular mycelium sending fingerlike 

 haustoria into the cells. Pale brown chlamydospores in the 

 tissues are not uncommon. The surface of the spots may show 

 a white mildew amounting sometimes to a dense felt, and a 

 similar growth is found in connection with spots which sometimes 

 develop on the unexpanded leaves, and show up later as rows 

 across the leaflets when these expand. 



The surface web or stroma may show only sterile mycelium 

 or may be abundantly covered with thick-walled brown chlamy- 

 dospores ; kept in a moist chamber it develops sporangia, 

 which are oval with broad prominent papillae, and when set 

 free are usually stalked. They are believed to liberate 30 or 

 more zoospores. Oospores have not been seen with certainty. 



The fungus corresponds with the description of Phytophthora 

 palmivora [Pythium palmivorum) Butler, the cause of the 

 destructive bud-rot disease of palmyra and coconut palms in 

 India, and its identity has been confu-med by E. J. Butler from 

 living cultures. 



Inoculations. 



An infection was secured on an unwounded leaf-base, re- 

 sulting in a spot two inches across and one inch deep, with 

 typical mycelium at its advanced margin. Developing in bright 

 weather the infestation did not penetrate to the leaf-base next 

 underlying in the ten weeks preceding its removal. 



The result of pouring suspensions of the fungus from cultures 

 into the hearts of trees 4-5 years old was the production of rows 

 of spots on the leaves next to emerge, but no further effect 

 followed. Complete artificial infestation of the husks of full- 

 grown green nuts was secured. 



Mode of Infection. 



Infection begins on young leaf-bases and often the fungus 

 penetrates several of these before reaching the bud, passing 

 inwards by a direct course. The rotting of the heart is accom- 

 panied by secondary bacterial infestation. No definite in- 



