Gums, Resins, 



[July, 1909. 



The perfected food materials are carried 

 down through definite channels in the 

 inner part of the bark by a stream of 

 sap which is entirely independent of the 

 upward stream. The system of minute 

 vessels which contain the latex or rubber 

 milk are entirely separate from both the 

 above mentioned sets of channels, and 

 have nothing to do with either of them. 

 The upward and downward streams of 

 sap are found in all trees, but latex 

 occurs only in a few. 



The evil results of ringing the bark, 

 or severing it by a cut which penetrates 

 to the cambium and extends right round 

 the tree, are primarily due to the inter- 

 ruption of the downward food supply 

 which must ultimately lead to the star- 

 vation of the roots and the consequent 

 death of the tree. Such ringing may 

 occur more or less completely as the 

 result of injudicious tapping. Auy cut 

 or prick which reaches the cambium 

 must sever a certain number of the 

 channels through which the sap passes 

 down to the r oots, and it is highly pro- 

 bable that the weakening effect of exces- 

 sive tapping is quite as much due to the 

 starvation of the roots as to the removal 

 of the latex. Any system of tapping 

 which involves the cutting or pricking 

 of the whole circumference of the tree 

 at one time is especially bad from this 

 point of view, and it must be considered 

 advisable never to tap more than a 

 third, or at the most one-half, of the 

 total circumference of the tree at any 

 one time. 



After a certain interval tapping may 

 extend to the untapped portion of the 

 circumference. This is owing to the 

 strong recuperative powers of the bark 

 or rather of the cambium. This im- 

 portant layer consists of a very delicate 

 tissue in which growth aud the forma- 

 tion of new and more permanent tissues 

 are constantly going forward. On the 

 outer side of the cambium, and conse- 

 quently on the inner side of the bark, 

 new additions are constantly being 

 made to the bark itself to replace what 

 is removed by ordinary wear and tear 

 or by the tapping knife. These addi- 

 tions include both new channels for the 

 descent of sap and new vessels for the 

 storage of latex, the two systems being, 

 as we have already pointed out, entirely 

 independent of one another. 



The latex tubes being entirely separ- 

 ate from the vessels in which the food 

 bearing sap is transported, the question 

 naturally arises what is their use to the 

 tree ? aud what is the precise function 

 of the milky emulsion of rubber which 

 they contain. This is a point as to 

 which we are still very much in the 



dark, From the fact that the great 

 majority of trees get on perfectly 

 well without any latex at all, we are 

 driven to the conclusion that this sub- 

 stance is not absolutely essential to 

 the life of the plant, and it is certainly 

 the ease that large quantities of latex 

 can be removed without causing any 

 visible injury to the health of the tree. 

 On the other hand, the latex is undoubt- 

 edly formed at the expense of valuable 

 food material, and the removal of latex 

 must thus indirectly cause a drain 

 upon the supply of food available for 

 the roots and for the purposes of general 

 growth. This drain is additional to 

 that check to the food current which is 

 caused by the partial ringing effect 

 which even the best tapping produces. 

 The amount of tapping which can be 

 safely carried out is therefore limited, 

 though only experience can decide the 

 point at which safety ends and danger- 

 begins. 



Even the most expert tapping is there- 

 fore dangerous if carried to excess. In- 

 expert tapping is attended with another 

 aud more serious danger in the injury 

 to the cambium which it involves. The 

 cambium is such an important part of 

 the tree that it is very desirable for the 

 planter to have a definite idea as to its 

 nature and functions. Situated as it is 

 between the wood and the bark, the 

 cambium is the seat of growth of both 

 these regions. Injury to the cambium 

 involves the cessation of growth at the 

 spot where the injury occurs, and since 

 only the younger portion of both wood 

 bark are active in the upward and down- 

 ward sap-transport already described, 

 any extensive injury to the cambium 

 involves serious damage to the whole 

 economy of the tree, quite apart from 

 the danger that the germs of disease- 

 may make their entry at the point of 

 weakness. 



Owing to the extreme thinness of the 

 cambium itself, injuries to this tissue 

 involve corresponding damage to the 

 outer part of the wood and to the inner 

 part of the bark. Taking first the case 

 of the wood, if the injury to the cam- 

 bium is not extensive, a renewal of 

 growth soon takes place and the in- 

 jured wood becomes buried beneath 

 fresh layers of woody tissue. By cut- 

 ting into the outer part of the wood the 

 traces of old injuries can often be 

 found. Injuries to the inner part of the 

 bark caused by irregular tapping are 

 often of a more serious nature, especially 

 when fragments of the outer bark or 

 other foreign substances are driven in 

 to the neighbourhood of the cambium 

 through in j udicious pricking. In this case 



