RUBBER (HEVEA) DISEASES 41 
that when a species is established in pure stands the conditions for 
the propagation of a parasitic fungus to which the species is sus- 
ceptible are greatly intensified. This is fundamental and is a con- 
dition long recognized in forestry practice. In the wild state noth- 
ing like the degree of infection observed in plantations is encoun- 
tered. This is attested by the fact that in the jungle- all trees, though 
they may have had the disease at different stages of their develop- 
ment, reach maturity without being seriously damaged. The natural 
jungle growth is a factor in this connection and serves as a screen 
against the wide distribution of spores locally and otherwise. These 
and other conditions pertaining to the natural habitat lead to the 
consideration of a possible plan whereby a natural stand of Hevea, 
if sufficiently great per acre, may be augmented by spot plantings 
and the area managed under improved estrada conditions. Owing 
to the influence of the natural jungle growth on air currents and the 
distribution of spores a state of equilibrium would be maintained. 
BLACK CRUST OF LEAVES . 
The fungus causing the black crust of leaves {Catacauma huheri 
(P. Henn.) Theiss and Syd.) is very widely distributed in the 
Amazon Valley, having been collected from Para to the highlands 
of Bolivia and Peru. It occurs in Dutch and British Guiana and 
in Trinidad. This fungus has not been considered of economic 
importance. Recently at several localities, notably at Tres Casas, 
Santa Laura, Democracia, Porto Velho on the Rio Madeira, at Cocal 
Grande near Obidos on the Amazon, and on the Rio Ouro Preto 
in Matto Grosso, it was found defoliating young seedlings. It was 
also very common at Itu in the Acre Territory and at Gobi j a and 
Porvenir in Bolivia. The immature leaves were rapidly parasitized 
and killed before the fungus could reach maturity. This resulted 
in reduced vigdr, with subsequent attack at the tops by secondary 
fungi. The fungus is very common on mature leaves of young 
stump shoots and of full-grown trees, especially in the denser parts 
of the jungle or when suppressed by a dense canopy of leaves and 
vines. The fungus is less common on Hevea planted in the open 
or on trees whose crowns project above the surrounding jungle 
growth. On several small plantations without intercrops the 
fungus was absent. From these observations it appears that the 
fungus would not be expected to be of importance on plantation 
rubber. 
Catacauma huberi, both in its early stromatic condition and later, 
is very conspicuous and easily recognized (PI. XVI). Shining 
black incrustations appear on the under side of the leaves, with 
corresponding yellowish spots on the upper side. The crusts are 
arranged in circles, sometimes separated by greenish zones, and 
inclosing a central stroma, or radiating outward from a common 
center along the veins form a network. Not infrequently the crusts 
are uniform in shape, without ramifications; and, in this state on 
casual notice, they may be mistaken for Dothidella ulei, with which 
this fungus is often associated. 
Even on old leaves the crusts are sometimes so abundant as to 
cause them to fall prematurely. In such cases the entire leaf be- 
