232 THE RUBBER TREE BOOK 



looked six months behind those in surrounding areas of exactly 

 the same soil and, otherwise, under exactly the same conditions, 

 proving that the roots of the kratok hindered the expansion of 

 the roots of the young Heveas and, by draining the soil of 

 moisture, hindered growth. In the opinion of the writer this 

 covering, therefore, cannot be regarded as a success, and any 

 very problematical gain obtained from the reduction of weeding 

 expenses is far more than counterbalanced by the retardation 

 of the growth of the trees. Kratok is a most difficult covering 

 to keep within bounds once it has been started. Unless con- 

 siderable care is exercised, and considerable expense incurred 

 in continually chankolling it back, it will encroach on the clear 

 circle usually preserved round the roots of the young trees. 



Crotalaria is another covering very similar to kratok in its 

 growth and conditions, and the same remarks apply word for 

 word. It grows to an even greater height, interferes with the 

 working of the estate, and gives vermin a very complete shelter. 



Mimosa is very largely employed in Sumatra as a covering, 

 and with much more success than any of the previously men- 

 tioned coverings. It is not the ordinary mimosa seen growing 

 wild along roadsides in Ceylon and Sumatra, but is grown from 

 seed procured from Java. So great has been the demand 

 recently for seed that prices are high and seed costs about 0.40 

 to 0.50 per picul. This mimosa branches well, and from a 

 single stem a covering spreads about 7 feet in every direction 

 over the surface of the soil. The roots go down about 6 inches, 

 and one can easily observe on them numbers of nodules, i.e., 

 bacterial gatherings. These nodules have valuable fertilizing 

 properties, and can also be seen on the root systems of dadaps 

 and many other leguminous plants. An illustration of these 

 nodules upon mimosa roots appears on page 22. 



It has been estimated that by ploughing in mimosa a very 

 considerable amount of nitrogen, amounting to about 200 Ibs. 

 per acre, can be added to the soil. By burning, much of this 

 is lost, but by no means all, as the nodules are on the small roots 

 of which many are left in the soil. 



The mimosa should be planted in belts down the centre of 

 the avenues between the rows of trees, and cut back from time 

 to time. Some planters allow the mimosa to overrun the whole 

 field, others try to keep circles clear round the trees. There 



