RUBBER (HEVEA) DISEASES 5 
composed of numerous trees of the same species is abundantly shown 
by the ravages of Dothidella ulei in the Guianas and in the lower 
Amazon, whereas the same fungus does not succeed in reducing the 
stand of Hevea in the natural forest. This leads to a consideration 
of intercrops. The gardener should plant other vegetables between 
his rows of cabbages, because it is known that the food requirements 
of the one are different from the others; in fact, the two crops may 
mutually benefit each other in various ways. One of the chief ob- 
jects to be gained, however, is the prevention of the spread of disease 
by growing on the same site various crops not all of which are at- 
tacked by the same disease. The principle is an old one, and its 
value in mitigating the effects of fungi has long been recognized 
in both field and forest. 
The success or failure of intercrops for Hevea will then depend 
upon whether they are equally susceptible to a particular disease 
or whether they are liable to overtop the Hevea in any stage of its 
early development. In the Amazon Valley the associated crops 
found in or around the small Hevea plantations either by accident 
or design consist usually of such plants as are attacked by the same 
class of root and stem fungi. (PI. I.) Since there has been no real 
attempt to establish plantations except in a small experimental way, 
the present account must be confined to calling attention to plants 
which would be undesirable for intercrops for the above reasons. 
Petch has called attention to the fact that cacao is undesirable as 
an associate crop for Hevea and enumerates several diseases common 
to both. These diseases, with one exception, are found on both 
Hevea and cacao in the Amazon Valley. They are Fomes liynosus, 
Diplodia theobromae, Phytophthora faberi, and Vstulina zonata. 
In addition there are the Kosellinia diseases and mistletoes. 
Caju (a common fruit of the Amazon), lime, orange, avocado, 
mango, and papaya were hosts either of parasitic or wound fungi 
found also on Hevea. The fungi were in most cases those already 
enumerated. Others of possible economic importance common to 
these hosts are omitted until there is an opportunity to study them 
in detail. Jungle trees carried a number of fungi found also on 
Hevea, notably Fomes lignosus, Poly poms zonalis, Ganoderma aus- 
tralis, G. amazonense, Poria vincta, Trametes floccosus, Nummu- 
laria anthracodes, and Vstulina zonata. 
Very few of the fungi enumerated are parasitic, but practically 
all are capable of continuous growth or indefinite hibernation in 
dead substrata and only await an opportunity to attack vulnerable 
parts of living hosts when favorable conditions arise. 
DESTRUCTION OF JUNGLE DEBRIS 
Owing to the fact that many of the important economic fungi 
attacking Hevea are common to the jungle and pass over from 
decaying or living forest debris to Hevea, the matter of the removal 
of this infectious material is of first importance. 
There is no reason to believe that the natural physical conditions 
for the clearing of land in the Amazon Valley are any more diffi- 
cult than in any other tropical region. It is not within the prov- 
ince of this bulletin to consider the cost of such an operation. 
Suffice it to state that every effort should be made to clear the land 
