Vol. XVI. No. 393. 



THE AGRICULTURAL NEWS, 



149 



Having now reviewed the matter, we will consider the 

 various points in the order in which they have been raiseH: — 



(1) To ascertain if there is i.n appreciable %'ariation in 

 the yields of individual trees over long periods. Messrs. 

 Morgan and ilarsden are agreed that no attempt has been 

 made to obtain reliable data as to the variation in yield of 

 latex and rubber fruni individual trees, nor is anything known 

 for certain as tn the regnlaiity in yield over a long period. 

 Mr. Morgan writes: 'All planters are fairly sure that some 

 trees arc better yielders than others at all times,' but also 

 agrees that 'yields may fluctuati',' Mr. Marsden is also of 

 the opinion that certain trees 'do yield well consistently 

 whilst from others the flow is always scanty.' Both Messrs. 

 Morgan and Marsden draw attention to the occasional heavy 

 yields from individual trees and suggest that such yields may 

 be due to disease, especially canker, which according to 

 Mr. .Marsden, in the early stages of attack stimulates the 

 latex flow. In any series of experiments it is therefore 

 necessarj' to examine the trees carefully to see that they are 

 healthy. 



(2) It being admitted that a variation exists to 

 determine how a classifica1;ioii of good and poor milkers can 

 be made, Mr. Marsden states that good milking trees are 

 known, but that for strict work it would be best to take the 

 quantity and quality of latex figures for at least a year. It 

 is certain that planters believe they can distinguish between 

 gO'id and poor milkers as on this depends the selection of 

 trees in thinning out. Mr. Marsden states that good milkers 

 are characterized by '(1) fewness of seed puds, and (:.') late 

 wintering.' If this be sr>, there would appear to exist the 

 same relationship between yields of rubber and seed in Hevea 

 as has been found to exist between yields of alkaloid and 

 seed in cinchona, and the same conclusion must apply, that 

 is to say. with the present haphazard system there will be 

 a tendency for the rubber-yielding capacity of the tree to 

 diminish, but that by careful seed selection, it should be 

 possible to raise the rubber-yielding capacity considerably 

 above the present average level. 



.Mr Morgan also refers to trees with a smooth bark of 

 a pink shade which are said to yield better than trees with 

 ordinal y bark. These trees are found growing in patches. 



(3) The collection of seeds from particular trees. 

 Mr. Marsden considers that this might be done by putting 

 bird netting over the capsules on one or two branches 

 (Jwing to the prevalence of pod disease (due to Phytophthora 

 faheri, see later) in Ceylon, it has been impossible to collect 

 really healthy seeds during the last few years. This disease 

 could be kept in check by continuous spraying over a small 

 aiea intended for seed collection. 



With further reference to the question of seed selection, 

 iMr Reeve has written the following report on the two points 

 rai.sed, i.e. — 



(4) To avoid cross-fertilization. 



(5) Assuming that both ma4e and female elements be 

 derived from good milkers, there would probably be poor 

 milkers among the ancestry. This would produce throw- 

 backs in accordance with Mendtl's law which might neces- 

 sitate selection over another generation. 



(4) To avoid crois-fertilizalion. — This difficulty could 

 be overcome by taking cuttings in the first fieneration. 

 A tree known as a good milker could be lopped and the 

 cutting planted in .some out-ot-the-way place away from other 

 rubber trees, preferably with a belt of jungle around. From 

 these cuttings, seeds would have to be saved and planted. 

 Allowing five to six years in Ceylon for the trees to come 



into bearing, the good milkers could be picked from the bad 

 and all the poor ones cut out. It would be necessary thea 

 to obtain seeds from the best milkers and plant separate 

 plots from each tree's seed. When these plots come into 

 bearing that with the least number of poor milkers could be 

 taken as the purest strain, and from this plot after cutting 

 out poor milkers the seed could be saved, knowing that such 

 seed will give, ou an average, .50 to 60 percent., perhaps more, 

 of good milkers. Xew areas would need to be planted fairly 

 thickly, and all poor milkers could then be cut out leaving, 

 say, 100 trees per acre known to be good milkers. 



Ee the point raised as to Mendelism. Is it definitely 

 known that the property of yielding an excessive quantity 

 of latex is capable of inheritance as a Mendelian character? 

 If this were so the establishment of a pure race of good 

 milkers would be comparatively simple. Consider the simplest 

 case of Mendelian inheritance, i.e., a cross between a pure- 

 bred good milker and a pure-bred bad one. The first gener- 

 ation would be good or poor milkers according to the 

 dominance of the latex-giving characteristic, i.e., if the good 

 milker were dominant, a hybrid of fairly good milkers would 

 result. From the impure hybrids on fertilization pure 

 strains and hybrids would result, and it would be necessary 

 to pick out the pure strains and breed from them. 



Probably nothing so simple would occur, and, as 

 Dr. Stevens suggests, there would almost certainly be a 

 certain amount of bad milking strain in the ancestry, which 

 would have to be eliminated by breeding. 



Even if the good milking characteristic did not follow 

 Mendel's law, it would probably be an inheritable fluctuation 

 which by selection could be improved. 



Rubber trees might also have been selected from a 

 known good milker giving, say, 8 BE), dry rubber per annum at 

 twelve years old with th-' average yield per tree at 6 ft), per 

 annum, and a breed of rubber trees could have been obtained 

 giving on an average, say, 7A S>. per tree per annum, thus 

 increasing yields 25 per cent. Such a procedure would have 

 been the correct one, and a fairly pare strain of good yields 

 could have been obtained in any twenty years starting from 

 the good yielding tree in bearing. Such experiments could 

 have been carried on indefinitely until a pure strain of good 

 yielders were obtained. 



Such a procedure is impossible now, and all that can be 

 done is to select seeds from good yielders; if fresh planting 

 is to be done, plant thickly and thin out poor yielders, where 

 necessary. Taking a widely planted area, say sixty trees per 

 acre, I think fully 75 per cent, of the seeds would be fer- 

 tilized from the pollen of the seed bearer, and only about 25 

 per cent, cross-fertilized from other trees, since an insect 

 once it arrives at a tree stays, and does not give itself an 

 unnecessary amount of flying. Such an area of older trees 

 with all bad milkers thinned out Avould give a fairly pure 

 strain of good milkers. 



Such a seed-bearing area would, however, need continuous 

 spraying during the S. W. monsoon in order to keep it free 

 from attacks of pod disease {Fhylophthora Faberi).* The 

 ordinary rubber areas are full of this disease, and I do not 

 think more than 1 per cent of the seeds can be considered as 

 good and plump, and fit for planting It is the exception ia 

 this district to pick up a really good seed when walking round 

 an estate. Naturally, isolation in jungle would partially 

 remedy this, in that spores would be filtered by the jungle,, 

 and wiih about one or two sprayings the area could be kept ■ 

 healthy. 



•*This refer.« to Ceylon. 



