RUBBER (HEVEA) DISEASES 31 
area. The disease was more severe in low-lying localities where the 
soil is damp and less apparent in well-drained sites. The mortality 
of the trees was not so much affected as were the quantity and quality 
of the latex produced. These experiments showed that after a few 
weeks a healthy bark renewal took place, but healthy action of the 
cambium and latex cells was seriously retarded by the injuries 
sustained. 
It was reported at Para that the most of the trees tapped by 
Akers died, and as a consequence the eastern tapping methods fell 
into disrepute. « 
It has not been possible to arrive at any definite conclusion as to 
the identity of the organism Akers found in the tapping wound \ 
His reference to the mycelium of a fungus appearing as a blue mold 
on the surface of the cuts may apply either to Diplodia or the bluish 
gray stage of a Phytophthora. Further investigations in the field 
will be necessary to determine this point. The fact that a Phytoph- 
thora is present on the leaves and fruits of Hevea in the Amazon 
Valley would indicate that the organism described by Akers may 
belong to that genus. 
Akers also refers to a canker found generally at the junction of 
the main lateral branches with the trunk and states that " the effect 
is to rot both branches and stem until the tree becomes exhausted and 
dies."' The opportunity was not afforded to determine the accuracy 
of this statement or the organism concerned. 
LICHEXS 
The smooth bark of Hevea is frequently covered to a greater or 
lesser extent with crust aceous or foliose lichens. The former are 
closely attached to the bark and appear more like green, yellow, red, 
white, or gray patches of paint than distinct organisms (PL I). 
They are usually inseparable from the bark. The patches may be 
isolated or run together, forming large areas with lobed or irregu- 
lar margins. The surface of these patches may be marked with 
slightly raised undulating tortuose or zigzag lines, small black, 
yellow, or brown dots, or cup-shaped bodies. The thallus of the 
foliose lichens is generally raised from and lightly attached to the 
surface of the bark. It often appears as a rosette with radiating 
segments and with lobed upturned margins. The colored lines, dots, 
and cup-shaped bodies are also present on the upper surface of the 
foliose lichens. They are the fruiting bodies of the fungous ele- 
ment of the thallus. 
The lichen crust or thallus is made up of chlorophyllaceous algal 
cells and the hyphse of various ascomycetic and basidiomycetic fungi. 
The algal cells are either regularly distributed or arranged in layer- 
in the mesh of the fungal hyphae. The result of this combination is 
to produce a structure closely resembling that of a true fungus. This 
is especially marked in the case of the hymenolichens. Here the 
fungous element is a Basidiomycete. and the resulting thallus is 
reflexed and applanate and resembles a green sessile Polystictu>. The 
lichen fungus in most cases is an Ascomycete. The thallus has a 
great variety of forms and may be a mere film on the surface of the 
bark of a much-branched structure resembling moss. 
