THE INDIA RUBBER WORLD 



[October 1, 1919. 



from individual trees. Sonic differences among latices arc very 

 apparent, such as color and concentration of the lale.x, and it is 

 more than probahle that the intrinsic value of the rubber from 

 one tree is better than that of its neighbor. For a thorough 

 consideration of the problem this point should be given allenlion, 

 though it is of less importance than the qucslions regarding 

 yield and disease resistance. 



METHODS OF IMPROVING STOCK. 



The methods whereby better planting stock can be produced 

 on the basis of the three points mentioned above may now 

 be considered. 



Seed Selection can never result in a uniform, highly produc- 

 tive plantation. The selection of seeds from trees, known to be 

 good producers enlarges the chances that the offspring will be 

 better yielders, than when the seed is obtained from unknown 

 parents. But the laws of heredity show that this is nothing 

 more th'an a chance, due to the number of generations of inter- 

 breeding and the cross-fertilization which takes plac^. 



The methods for improvement based upon scientific principles 

 present themselves as follows: 



1. Breeding. 



2. Seedling selection. 



3. .*\rtificial propagation. 



Breeding. In order to obtain a better strain through this 

 method, it is necessary to isolate a single strain, which will 

 breed true to type. Through cross-fertilization during a large 

 number of generations, the present plantation rubber tree is of 

 a very comple.x nature, and to isolate such a strain in a systematic 

 way involves a great amount of work, to be divided over a large 

 number of years. This is the more so because three different 

 characteristics are involved, namely: yield, disease resistance 

 and quality of the rubber. As a tree has to be grown for at 

 least four years to determine the single factor of yield, it will 

 easily be understood that the problem of breeding a really 

 valuable strain will take more than one generation of investi- 

 gators. 



That scientific breeding experiments should be carried out is 

 certain, but this should be done by the various governments 

 concerned ; for any private concern this method is entirely too 

 costly and requires too much time for any immediate com- 

 mercial purposes. 



Seedling Selection. There is no way to select in the nursery 

 the seedlings which will later develop into big producers that 

 will be immune to disease. No morphological character is known 

 correlated to yield, .^s a result of extensive experiments along 

 this line with fully grown Trees I am satisfied that shape and 

 size of leaves, mode of branching, color and texture of bark 

 and similar characteristics are not correlated to yield. There is 

 a possibility that histological characters, such as distribution of 

 latex, vessels, their number or size, may furnish a clue to 

 productivity, but as we are dealing with seedlings, these would 

 have to be destroyed or at least seriously damaged before their 

 value was known. While of course it is best to select the most 

 vigorous seedlings for planting out, still this is not the solution 

 to the problem. 



Artificial Propagation. This is the method used by pomol- 

 ogists to perpetuate the strain or variety, which has proved 

 valuable. The varieties of apples, pears and other fruits were 

 originally obtained through cross-breeding, a procedure, which, 

 for immediate results, is out of the question for Hevea, as has 

 been pointed out above. For stock we have to start with the 

 trees now on the plantation. AwA it is a sure fact that enough 

 material is there to produce something much more valuable than 

 the average we have today. 



PROCEDURE TO BE FOLLOWED. 



In order to obtain the best stock the following procedure 

 should be followed : 



1. Select a number of the oldest trees to be found, growing 



under the same conditions regarding soil and climate as those 

 prevalent on the new plantation. 



The oldest trees should be selected, because they have been 

 under observation for a longer period than the younger ones 

 and more is known about their yield and disease resistance. 

 They should be chosen from a locality where soil and climatic 

 conditions are as nearly as possible the same as those on the 

 contemplated plantation, because a certain variety may prove 

 excellent in one soil, while it would not be in another; it may 

 grow well at a high altitude but break down in the lowlands. 

 The argument sometimes put forward that selecting seed from 

 a place where conditions are entirely different from those on 

 the new plantation will result in better trees, is entirely without 

 any scientific foundation. 



2. Of the trees selected, choose those which show no evidence 

 of ever having been attacked by disease. 



The chance for immunity to disease is greater in such trees. 

 This of course does not mean that these trees will never contract 

 any disease ; it simply improves the chances for a disease-proof 

 offspring. 



3. Of the remainder select the highest yielders. 



To determine which is the best yielder, it is necessary to 

 measure the dry rubber yield for an extended period, preferably 

 one year. 



4. If two or more trees yield about the same quantity, the 

 choice should fall on the tree producing the best quality of 

 rubber. 



This point is of less importance than yield and disease resist- 

 ance, unless very great differences should be found in the 

 course of the experiment. 



METHODS OF ARTIFICIAL PROPAGATION. 



These may be divided into two groups, those providing for 

 their own root systems and those where one tree is grafted 

 upon another. It is probable that the root system is as important 

 to latex production as are the parts above the ground. 



Methods for developing root systems include marcotting and 

 cutting. The first method, marcotting ("tjankok"), has been 

 successfully carried out in the experimental garden at Buiten- 

 zorg, Java. It is a laborious method, however, and should be 

 used only if every other method fails. 



Cuttings were made from the first seedlings grown at Kew 

 Gardens and shipped to Ceylon, and it can be done again. These 

 cuttings carry with them the characteristic root system of the 

 parent tree. This root system is a suitable one for a good 

 producer inasmuch as the parent tree was selected for its 

 productivity. It is barely possible that a less perfect root system 

 will develop from cuttings and this should be investigated. If, 

 however, cuttings develop a good root system, this method 

 is to be preferred above any other method of artificial propaga- 

 tion. It is speedy and above all simpler than grafting, and can 

 be carried out by native labor with a minimum amount of failures. 



Methods whereby a good-producing, disease-resistant variety 

 is grafted upon another root system are numerous. One of 

 the simplest has been carried out on a larger scale lately on one 

 of the Sumatra plantations and has proved quite successful. 

 This method is budding. However, when resorting to grafting 

 the thing to bear in mind is, that not only should all possible 

 attention be given to the derivation of the bud or scion, but 

 the stock used to graft upon should be carefully selected. Other 

 qualifications enter into the selection of this stock than into the 

 selection of the bud or scion. The most important is to select 

 young trees free from any root diseases and those with the 

 best-developed root systems. The stock can very well be grown 

 from seed, but none except those having the above-named 

 qualifications should be used to graft upon. 



Summarizing the foregoing paper, it is found that : 



1. The present method of reproducing Hcvea should be dis- 

 continued. 



