420 
UKrOKT OF CHEMICAL LAHOllATOUY 
Moisture 
Protection 
from fire 
Tapping 
Physical analysis of the sample could not be made, as it was lost in the recent fire 
which destroyed a portion of the Laboratories. 
It will he noted, that while both lime and magnesia are present in these soils in hut 
small amount, the })roportion of the latter to the former is relatively great. 
There is nothing in the figures just given to show why the soil in these depressions 
should not supjjort hashab trees equally as well as the soil of the geneinas. It was thought 
that the exjfianation of their absence would be found in a higher proportion of soluble 
salts accumulated in the lower levels, but examination proved these to he practically absent. 
In spite of the obvious poverty of “ geneina ” soils in Kordofan, it may he of interest to 
note that they are found to bear fair crops of millet, sesame, earthnuts, etc. 
Moisture. Hashab trees in soil well supplied with water during the dryer season fail 
completely to yield gum. In this respect these trees differ markedly, e.;/. from ^1. aruljica 
(sunt) trees, which by tapping may be made to yield gum, even when situated close to the 
river, with roots well supplied with moisture and the tree covered with green foliage. 
The largest yield of gum seems to result from a good rainy season followed by one 
exceptionally hot and dry. 
rrotectioH from fire. Experience has shown that the scorching of the trees resulting 
from a fire in the undergrowth renders a geneina unproductive for the season. This is 
quite in accoi'dance with the bacterial explanations of gum production, the microbes 
being destroyed by the heat and the geneina more or less sterilised. 
Tii.ppiiKj. It has been noted that, in tapping, strips of 2 to 3 feet in length and 
1 to 3 inches in width, more or less, according to the size of the branch ojierated upon, 
appear to give the best results. When longer strips, 6 feet or more, were torn off, less 
gum exuded, and there was the additional disadvantage that the tree was unnecessarily 
weakened. Injury due to injudicious barking is often very great. The workers have 
found that even when the usual method is employed the tree will not stand tapping 
more than once every alternate year. In order to determine whether the injury due to 
barking might not be lessened, the experiment was made of tapping by a number of 
short cuts without removal of the bark. By direction of the Director of Woods and 
Forests, Mr. Bisset, the Deputy Inspector of this district, also had a number of trees 
tapped by removing shorter strips of the bark than is the usual practice. The total 
yield of gum per tree for the entire season of collection is given in the table below, in 
which is included, for conqiarison, the average yield from small, medium-sized, and 
large trees in neighbouring gardens, tapped in the ordinary manner. The weights of 
gum are given in rotls, which may be taken roughly to equal pounds. (2-166 rotls = 
1 kilogram.) 
Garden of 
Method of Tapping 
Size of Tree 
Avera 
ge Yield of Gum 
per tree 
Ali Niir-ed-Diu 
Ordinary 
Small. 
0*75 
rotl 
jj «• • • • • • • • 
r^IediuDi 
1-33 
}J 
. 
Large. 
1-90 
Peki Wad Bollal 
Short strips ... 
Smaller 
U-52 
>> 
» . 
Larger 
... 0-87 
Adam Afifi 
Ordinary 
Medium 
0-90 
>> 
n 
Xuinerous cuts without removal of bark 
»> • • • 
0-28 
>5 
