72 liKPOHT OK CIIEMTCAL LArWHATOHV 



(i-) rf fduiid feasible it would <i])])('ar profi^-ahlo to tap lightly, but in a considerable 

 iiuiidiei- of places, on eacli tree, in ordin- tbat tlie t,'uin may form separate tears, instead 

 of runnint; down tlie trunk in a tliin layer. It is probable that this latter condition 

 would be less likely to olitain if the tree were tapped, as suggested, towards the end of 

 the dry season, when the gum might be expected to exude in a less liquid condition. 

 Such gum might form tears less contaminated by bark and more easy of collection. 



(/) As regards the marked effect of the application of chemical agents to the freshly 

 tapped surface, it seems reasonable to conclude that tlieso act, not by inciting gum 

 formation, but rather as irritants, stimulating the How of gum-containing sap to the 

 part. In other words, it seems likely that the gum already existed in the sap, the trees 

 having |)i-eviously become infected by the entrance of the microbe at other points. This 

 conclusion is supported by the fact that, of a further lot of twenty trees, treated in the 

 same way by the forest ofTicer, a few failed to respond. 



The above results, obtained in Sennar, were comnninicated to Mi'. E. 8. I'ldie, who 

 was working ai. th(^ sanu^ time on similar lin(is in Kordofan, but on tlie /idnliiih tree. 

 As will be seen from liis report (/«/;/!■ 7.'i), Mr. I'ldie's observations led him to tlie same 

 conclusions. 



To conclude these notes, the fact that in the neiglibourbood of Saoleil, only siicb 

 trees as had been injured by fire yielded gum readily on tapping, is a point of obvious 

 importance. As already noted, it still remains to be determined whether the soimder 

 trees could be made prochietive if tapped towards the end of tlu! Iiot dry season. If 

 not, we would be compelled to rely upon injured trees for j^um production, and, in tliis 

 case, a method of reducing vitality more under control than a chance forest lire, is 

 obviously desirable. Girdling some of the roots of tlie tree, or, more simply, partial 

 girdling of tlu^ trunk near its basi! would siicm to be a promising method. Objection 

 may be raised that it is not advisable to carry the injury to such an extent, but since 

 these trees are at present ])ut to no use and have cost the Government no inconsiderable 

 sum for lire ])rotection, such an objection does not appeal to one as sound. 



The metliod, if found to answer, might be advantageously used to secure at the 

 same time a cheap wood fuel which is even more desirable than an increased output 

 of falli, gum. The trees might be utilised for gum as long as the work appeared profitable, 

 aft(!r wliich tlie\' could l)i' fi'lled I'oi- use as fuel, 



