64 BULLETIN 1380, U. S. DEPARTMENT OF AGRICULTURE 
Pruning should be done when the trees are wintering or when 
growth is at a standstill. At this time there is less water in the 
wood and the wound is not so liable to infection. The chief reason 
for pruning at this season is that antiseptic substances applied to 
the wound are more readily absorbed. If the surface of the wound 
is moist, such substances do not penetrate the wood and may later 
flake off. allowing water and spores of fungi to enter. 
The artificial removal of branches that had developed low on the 
trunk was observed at Para and Manaos. In practically all cases 
the branches had been cut off several inches from the trunk. The 
projecting dead stubs were infected with fungi and in two cases with 
species of considerable economic importance. 
It is sufficient to state that the modern practice is to cut off the 
branch as close to the trunk as possible. Projecting stubs soon die, 
since they are no longer supplied with food. Infection sets in and 
may spread to the living tissues of the branch collar. Eventually 
the stub decays, and the rot advances into the parent stem. The 
effect is the same as that described for naturally pruned branches, 
and the same set of fungi is concerned. 
Lightning injury. — Lightning injury of Hevea in the Amazon 
Valley was demonstrated in but few cases. On a small tree about 
9 inches in diameter near Biberalta, Bolivia, small black scars were 
distributed over the main part of the trunk in considerable numbers. 
On another tree strips of cortex about half an inch wide were sepa- 
rated from the wood. These strips were not continuous, but ap- 
peared on different sides of the tree. Some of the topmost branches 
were dead, but otherwise the health of the tree appeared in no wise 
affected. These longitudinal wounds were almost closed with a 
healing callus. The small spot wounds in most cases were com- 
pletely healed. The dead edges of the cortex extended partially over 
the renewing callus and when removed exhibited a smoothly healed 
surface. This was in contrast to the reaction from excessive tap- 
ping and is explained by the small extent of the original injury. 
The wounds were of a uniform depth and involved from one to 
two annular rings. The edges of the rings were slightly separated 
from those beneath and the space plugged by a small secondary 
callus. Otherwise the process of healing was the same as that in 
injuries from other causes. 
If the tree is struck during the growing season the influence of the 
shock on its growth is usually expressed by the modification of the 
cells of the annual ring of the season, so that the continuity of 
the normal structure of the wood is broken. This makes a possible 
defect in the wood when the trunk is forced to sustain heavy loads, 
as in the case of high winds. 
FIRE INJURY 
On a small plantation near Para trees injured by fire from the 
burning of grass or other materials along the edge of a clearing were 
examined. 
Although bark is a poor conductor of heat, the normal thinness of 
the bark of Hevea makes it very susceptible to fire injury. The 
younger the tree the more serious the injury. 
