RUBBER (HEVEA) DISEASES 55 
root system. The berries may also fall to lower parts of the tree 
from the infected branches higher up, or they may be carried by 
animals. Trees of all age classes are liable to infection, provided 
the mistletoe seeds reach parts of the host not yet protected by ma- 
ture cortex. The parasite may spread from the original point of 
infection into older cortical tissues which are not liable to infection 
from without. Excessive mistletoe infection of the lower branches 
of Hevea may cause the upper portion of the crown to die, giving 
rise to the phenomenon commonly called staghead. Severe infec- 
tion throughout the entire crown may result in a reduction of yield 
and eventual death of the tree (PL XXVI). Infection on the 
branches causes the formation of abnormalities and the death of the 
branch beyond the point of infection, leaving club-shaped stubs 
(PI. XXVIII, A). Infection on the main stem at an early age 
results in the formation of burls (PL XXVII) and contorted trunks 
(PL XXIX, A and B). The weakening effect of the formation of 
these burls is often responsible for the infection by Nummularia 
anthracodes and other weak parasites and insects. 
The mistletoe next in importance on Hevea is Phthirusa hrasili- 
ensis. This is a leafy species and for that reason is often very con- 
spicuous when perched high in the crown of its host (PL XXVIII, 
B). Young Heveas have been observed to support a colony of this 
mistletoe after the parasite had caused the death of all parts of its 
host above the seat of infection (PL XXVIII, C). This illustrates 
a very interesting relation between host and parasite. The host, 
however, must eventually succumb to the attack. 
Although mistletoe was common on Hevea in the forest it is 
not likely to be of much consequence on plantations. The parasite 
may be controlled by keeping a sharp outlook for early infections 
and removing the infected branches. This will prevent a center 
of infection from forming in the plantation. The action of the 
parasite is slow except on young trees, and before any serious dam- 
age results the infections may be removed. Mistletoe infections on 
associate crops should be eliminated; likewise, those on surrounding 
forest trees if the species prevalent is prone to attack Hevea. The 
parasite dies with the death of the host; hence, it is not necessary 
to burn lopped infected branches except from the standpoint of 
general sanitation. 
The mistletoes in the Amazon Valley are subject to various 
fungous diseases, and the leaves and stems support a number of 
mosses, lichens, and alga?. Xone of these organisms, however, 
greatly affect the vigor of the parasites. 
It is interesting to note that the seeds of some mistletoes found 
on Hevea and jungle trees contain as high as 20 per cent of their 
dry weight of almost pure rubber. The practical significance of 
this fact was discussed by Warburg in the Tropenprlanzer in 1905. 
DAMAGE CAUSED BY LIANAS AND OTHER VINES 
Lianas and other vines occasionally cause injury to young Hevea 
in the jungle by winding around their trunks. As the tree increases 
in thickness the cortex is subjected to pressure, with the result that 
the vertical descent of food substances is forced to take a spiral 
course. This causes the transporting tissues to change from the 
