April, 1910.] 



295 



Saps and Exudations. 



growth in thickness would be greatly 

 retarded if the trees were allowed to 

 continue so crowded, consequently thin- 

 ning has had to be practised. Wider 

 planting is now more generally under- 

 taken, and a distance apart of twenty 

 feet (100 trees per acre) is commonly 

 followed. Even at this interval the 

 shoots of adjoining trees will often be- 

 gin to interlace in five or six years' time, 

 about the period when tapping can be 

 commenced. Judicious thinning might 

 be started now by removing the least 

 desirable trees after thoroughly tapping 

 them. 



The correct planting distance to be 

 pursued is still an open question. Time 

 will doubtless show whether room for 

 the ultimate possible extension should 

 be provided at the outset, or whether 

 a closer distance should be adopted 

 while the trees are young, to be follow- 

 ed by thinning later. In the latter case 

 probably more rubber may be obtained 

 per acre during the first couple of years 

 of tapping, but this may be at the 

 expense of future yields. The present 

 view appears to be rather that within 

 reasonable limits a closely planted acre 

 of rubber is worth no more than, if 

 as much as, a widely planted one. 



Straight v. Forked Trunks.— Since 

 tapping is usually confined to the basal 

 six feet of trunk, and since trees which 

 fork early have generally a greater 

 basal girth than those of the same age 

 which remain straight, attention has 

 been turned to the desirability of 

 artificially inducing trees to fork early, 

 in order to hasten their increase in 

 girth. This can be accomplished with 

 the least injury and trouble by what 

 is known as "thumb-nail" pruning. 

 The terminal bud is pinched out when 

 the youug tree has reached a height 

 of about ten feet; forking then takes 

 place, and further pruning can be prac- 

 tised if necessary to reduce the number 

 of main branches. Wickham strongly 

 recommends this practice and considers 

 the ideal tree-form for Hevea to be three 

 main primary limbs, and to each of 

 these three secondary branches— nine in 

 all. Wright* also favours it, though 

 pointing out that it is unwise to practice 

 it on trees growing in a light soil and 

 exposed situation, for they would in time 

 be liable to be blown oyer by strong 

 winds, owing to the weight of leaf 

 canopy produced ; they would, in fact, 

 be more top-heavy than unforked trees, 



* H. Wright, Hevc'i brasiliensis or Tara rubber, 

 3rd edition, 1908, 48-51. 



l J etch,t Mycologist to the Ceylon 

 Government, fears that such treatment 

 will favour the entrance of the fungus 

 Corticium javanicum, a somewhat 

 dreaded bark disease. Ryckmann states 

 that in Java and Sumatra this fungus 

 attacks chiefly the forked trees, either 

 natural or induced. The cleft affords 

 a lodging-place for spores. A split in 

 the wood is liable to occur here through 

 wind or other causes, thus allowing 

 the entrance of the fungus-hypha?, and 

 so the commencement of disease. 



Catch Crops.— Asa newly-planted area 

 of Para-iubber will give no return for 

 at least five or six years, and as between 

 the widely planted trees there is much 

 unoccupied grouud. some profit may be 

 immediately secured by growing what 

 are called catch crops. Though their 

 cultivation may lead to the payment 

 of small dividends before the rubber 

 comes into bearing, their value is to 

 some extent doubtful, as these inter- 

 planted crops frequently retard the 

 growth of the rubber trees. Cassava 

 {Manihot utilissima) has been largely 

 used, but it is hardly a desirable plant 

 to employ, as botanically it is too nearly 

 related to Hevea. A disease or insect 

 enemy which attacks the one will most 

 likely spread to the other. The subject 

 of catch crops and their undesirability 

 is dealt with fully in Wright's book.; 

 There is much to be said for and against 

 their cultivation. 



Protective Belts, — A large uninter- 

 rupted area, occupied by a single species 

 of plant offers a most s'uitable field for 

 the spread of a fungus or an insect 

 foe. There is nothing to check a disease 

 commencing atone point from spreading 

 rapidly over the whole plantation. 

 Consequently a system of blocks, separ- 

 ated from one another by screens 

 composed of other trees, is recommended 

 for rubber estates. A disease or pest 

 observed in one block might then be 

 overcome before it had time to pene- 

 trate to a neighbouring area. 



These protective belts may be formed 

 by the retention of strips of the virgin 

 forest, or they may be planted specially. 

 If the latter course be adopted, trees of 

 economic importance should, if possible, 

 be chosen, care being taken not to select 

 any nearly related to that composing 

 the main cultivation. For example, 

 Castilloa or Ficus might be used in 

 connection with Hevea. thus a f fordin g 



t Petch. Circular and Agricultural Joiunal, 

 Royal Botanic Gardens, Ceylon, 19<>9, No. 21, 

 Vol. iv., p. 193. 



% H. Wright, Hevea brasil'ensis or Para rubber, 

 3rd edition, 190«, 51-6. (The Standard work on 

 rubber cultivation.) 



