4 i2 SCIENCE PROGRESS 



habitat of the plant, and yet be ineffectual against other 

 enemies which the species may meet in a new environment 

 The theory of water-storage and conduction is perhaps 

 the most plausible. The watery nature of the latex in 

 the tree trunk of Hevea has been noticed to be affected by 

 the state of the soil. When dry, the latex is thicker and 

 flows out less readily, suggesting that the tree is drawing 

 upon the reserve of water accumulated in the laticiferous 

 tubes. In the alluvial regions of the Malay States the tree 

 yields latex very abundantly. Here there is a surplus of 

 moisture in the soil, and so the tubes are always well 

 distended with latex. There is, in fact, no need to draw 

 upon this reserve. 



The removal of latex from the Para-rubber tree appears 

 to have little or no detrimental effect. A young tree 

 judiciously tapped continues to grow almost as well as 

 one which has not been touched. Some observations made 

 by Macmillan and Petch 1 have shown, however, that the 

 seeds from tapped trees are, on the whole, lighter in weight 

 than those from untapped ones. Any prejudicial effect of 

 the tapping is probably due rather to the injury to and 

 removal of the surrounding tissues than to the extraction of 

 the latex itself. 



Tapping- Systems. — The demonstration of wound-response 

 quickly influenced the method of tapping Hevea trees fol- 

 lowed in the East. To gain the full benefit of this response, 

 the new incision must be made quite near the previous one. 

 Thus was suggested the feasibility of reopening the old 

 wound, rather than of making a fresh incision. Experience 

 has shown that very satisfactory results can be so obtained. 

 A thin paring of bark is removed from the lower edge of 

 the initial groove at each subsequent tapping. By this 

 means the bark down to the cambium is gradually shaved 

 away. Thus excision instead of incision has come to control 

 the tapping systems now in vogue. 



The original small V-shaped cut has been completely 

 abandoned. Attention to wound-response showed that a 

 single slanting cut served just as well. Oblique incisions 

 form the basis of the methods of tapping in use. 



At first the latex from each incision was collected separately. 

 1 Macmillan and Petch, Circular, Roy. Bot. Gardens, Ceylon, 1908, vol. iv. No. 11. 



