RUBBER PLANTING 49 



spiral system of tapping has been continued for years 

 without any perceptible injury to the trees. Neverthe- 

 less, human skill is never perfect, and any false cut, even 

 if it just misses the cambium, may sever some of the 

 conducting tubes. This danger is clearly increased 

 when a large part of the circumference is tapped at 

 one and the same time. For this reason we do not 

 recommend the spiral system of tapping to those com- 

 mencing work on new estates. 



Fitting has also studied the effect of tapping in 

 depleting the food supplies stored up in the bark. He 

 found a marked reduction in the amount of starch 

 present in the cells around and especially immediately 

 below the wound, after paring had been carried out for 

 some time. This fact suggests that food materials are 

 rapidly used up in the neighbourhood of the wounded 

 area. It may therefore be concluded that the removal 

 of large quantities of latex will tend to produce partial 

 starvation of other parts of the tree, an effect quite 

 distinct from any mechanical injury. 



Renewal of bark. 



The bark is constantly undergoing increase in thick- 

 ness owing to the activity of the cambium. As the 

 phloem tubes grow older their functions are given up, 

 and their place is taken by the younger elements within. 

 A considerable part of the older phloem and medul- 

 lary rays becomes converted into stone cells, which 

 L. 4 



