140 
about is also good evidence in favour of this conclusion. Their 
occurrence on untapped trees, however, and on untapped parts of old 
trees precludes any assumption that they are produced solely as the 
result of previous injury, while the fact that they occur on all classes 
of soils in the Federated Malay States is sufficient to do away with 
any theory of their being connected with nutrition. 
With these considerations in view we are led to the assumption 
that they are the result of a natural habit on the part of the plant 
and that their development is in some considerable degree stimulated 
by wounds produced in tapping. Some individual plants tend to 
produce burrs in larger quantity than others, while other plants, » 
which are grown under the same conditions of soils and illumination 
and to which similar treatment has been extended in tapping, are 
apparently altogether free from burrs. The question of the heredi- 
tary transmission of the capacity for producing burrs has already 
been raised by Petch, and it would appear to be distinctly within the 
realms of possibility. For this reason Petch has suggested that the 
selection of seed for planting should be confined to trees which do not 
produce burrs. It is proposed to carry out experiments on as large 
a scale as possible for the purpose of testing the hereditary trans- 
mission of the character of burr-forming ; it will, however, be many 
years before any conclusions can be arrived at. For the present it is 
advisable to avoid selecting seed from burred trees or, at any rate, 
from areas which contain badly burred trees. 
If direct treatment is to be applied to burred trees the burrs 
must be removed early. Wlien they are small and pea-like they can 
be easily removed by a pocket-knife. As they get larger they require 
to be carefully cut out so as to cause as little damage as possible to 
the adjacent tissues. When they have once commenced to fuse with 
the main wood removal is out of the question. The wounds produced 
by removal of burrs maybe left unprotected. Attempts are made 
in some places to seal them with a mixture of cow’s dung and clay ; 
this, however, appears to be quite unnecessary, if they are removed 
when they are young the wounnds left after removal are no more a 
source of danger to the plant than ordinary good tapping, is. 
Burrs of the Second Type. 
i 
Whenever, in tapping, the cut of the knife descends too deeply, 
severs the cambium and wounds the wood, and irregularity of 
surface is produced on the renewed bark. Cases of this are more 
commonly met with in older tapping, but they are not wanting even 
in tapping of the present day. 
When these swellings occur in large numbers on the tapping 
surface they resemble scars left by the removal of branches. 
If the bark from such a swelling is taken off the surface of the 
wood beneath is seen to be raised. To examine this more carefully 
* it is necessary to consider what happens when the wood of the tree 
is wounded. The exposed cells of the wood become brown and the 
