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 Fetch, and it would appear to be distinctly within the 

 realms of possibility. For this reason Fetch 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. When 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. 



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 



