024 REPORT OF THE HARVARD AFRICAN EXPEDITION 
age the blackening becomes evident externally, the lines elongating and tending 
to fuse, thus forming a darkened area with a ragged diffuse outline. In wet 
weather this blackened surface is covered with a white cottony layer in which 
the zoosporangia of Phytophthora are produced. These symptoms are in very 
close agreement with those described by Petch ! for black-thread blight of Hevea 
in Ceylon, caused by Phytophthora Meadii. He also states that this fungus 
attacks the fruits first and from these the leaves are infected, and from the leaves 
the fungus is spread to the wounds made by tapping. An additional species 
P. Faberi Maubl. is recognized as causing the garnet red discoloration of Hevea 

No. 410. — Phytophthora Meadit, the cause of the black thread blight, showing 
the discharged sporangia and their variation in size, x 1000 
bark. The separation of these two species has been questioned by Ashby * who 
places both forms in the “rubber group”’ as a strain of P. palmivora Butler. If 
such is the case, then this organism has dangerous potentialities should it by 
chance follow the same trend that it has followed on cacao in Trinidad. Although 
the writer does not wish to be an alarmist, it certainly seems decidedly worth- 
while to investigate further the pathogenicity of this fungus in relation to Hevea, 
especially since a count at random showed nine out of thirty-nine trees, or twenty- 
three per cent, to be infected. In addition to Phytophthora, there also was present 
with that genus, a species of /usarvum of which both the micro- and macrospores 
were found. It seems quite probable, however, that this is secondary, and may 
even lead a saprophytic life on the small amount of latex remaining, yet in view 
of the parasitic nature of the genus, this too deserves attention. 
1 Petch, T.: The diseases and pests of the rubber tree, pp. 119-133. Figs. 18-14. London, 1921. 
2 Ashby, S. F.: Trans. British Mycological Soc. 14:18-38. 1929. 
