3*4 



The fact that incisions made near the ground in Hevea produce 

 more latex than exactly similar ones made at a height of two or three 

 metres can hardly be explained otherwise than by the tension of 

 the tissues at different heights. H. L. 



The importance of the action of tension in the tree as producing 

 a flow of latex cannot be overlooked. In a normal state the tension 

 varies at different times of the day, gradually diminishing from the 

 morning to midday, and to the early part of the afternoon, when 

 it is at its minimum. It then commences to increase continuing 



.... o 



through the night and attaining its maximum at dawn. These 

 variations correspond to the variations in transpiration of water. 

 During the night the transpiration lessens so that the pressure of 

 the w r ater increases in the stem, during the day the transpiration 

 increases to its maximum in the afternoon and with the lessening of 

 the amount of water in the stem comes the lowering of the tension. 

 Now we know that the flow of latex from the cuts in a Hevea in- 

 creases just in those hours at which tension is greatest and trans- 

 piration least. The flow during the day is usually slight. It in- 

 creases if the cuts are made towards evening and the greatest flow- 

 is obtained in the early morning. 



Besides the regular diurnal variations in tension, there is also an 

 annual periodicity at least in temperate climates. The tension in- 

 creases in the spring till the summer. This increase being due to 

 the thickening of the new wood and the drying and contracting of 

 the outer layers of the bark. In our climate unfortunately little 

 has been done to investigate the periodicity of growth of trees. 

 The Heveas however in May just before they flower do shed all 

 their leaves, and it is probable that at this time the tension is least ; 

 corresponding to the relaxation of tension in the winter season in 

 colder climates. Experiments in this are much to be desired. In 

 one or two cases owners of Hevea trees have reported that little or 

 no latex flowed when the bark was cut, w T as it possible that in these 

 cases the tension was not sufficient for some reason or other to 

 force out the latex ? 



In tapping a tree in the Botanic Gardens, it was observed that 

 the bark seemed loose, i.e., not so firmly attached to the wood as is 

 usual, this tree produced very little rubber, and though the tree 

 was apparently healthy in other respects, it was probably sick. The 

 looseness of the bark whatever the cause was, might be taken to 

 show that the tension was at a minimum, and that alone would ac- 

 count for the feeble flow of latex. 



H. N. R. 



THE PENANG GARDENS RUBBER TREE. 



Plate v. 



The Para rubber tree growing in the Waterfall Botanic Garden, 

 Penang, to which reference has been made in successive Annual Re- 

 ports on these Gardens since 1888. showing the result of six tap- 

 pings, was one of about two dozen young plants received from the 



