September, 1910,1 



197 



Saps and Exudations, 





Daily Tapping, 







No. ot 



No. of 



No. of 







Experi- 



trees 



times 



Yie 



Id. 



ment. 



Tapped. 



Tapped. 



lbs. 



oz. 



I. 



50 



127 



247 



1 



T r 

 11. 



120 



36-3 





19 



III. 



140 



34-1 



68 



2| 



IV. 



200 



110-2 



674 



9f 



V. 



200 



80 



453 



8| 



VI. 



150 



73-4 



680 







860 



75 



2253 



9| 



Alternate 



No. of 

 Experi- 

 ment. 

 I. 

 II. 

 III. 

 IV. 

 V. 

 VI. 



No. of 

 Trees 

 Tapped; 



120 

 140 

 120 

 200 

 150 



730 



Day Tapping. 

 No. of 

 Times 

 Tapped 



Yield, 

 lbs. oz. 



56-3 



46-5 



18 



19-8 



32-6 



308 

 264 

 99 

 195 

 187 



32-3 1,055 0£ 



Prom this it may be calculated that 

 if 730 trees tapped on alternate days 

 32 - 3 times yield 1,055 lbs. of rubber, 

 then 860 trees tapped on alternate days 

 75 times will yield 2,797'2 lbs. of rubber. 

 Therefore the alternate day tapping 

 shows a gain of 54Slbs. over the daily 

 tapping, or about 24 per cent, in spite 

 of the poor yield of the alternate day 

 tapping in Experiment VI. But it must 

 be remembered that this is chiefly 

 arithmetic, and that it is supposed that 

 both systems of tapping are carried on 

 to the same number of tappings, i.e., 

 that the daily tapped trees are " rested " 

 half the time. 



WEAK RUBBER: THE LATEST 

 EXPLANATION. 



By T. Petch, b.a., b.sc 



In Science Progress, April, 1910, Parkin 

 suggests that the reason why rubber 

 from young trees is weaker than rubber 

 from older trees may be due to the fact 

 that the former may contain a large 

 proportion of rubber formed in " pri- 

 mary growth," and that this rubber 

 may be weaker than that formed in 

 " secondary growth." "In such young 

 trees the primary laticiferaus tubes will 

 still be yielding some latex, which will 

 mingle with that from the secondary 

 tubes, giving an intermediate product." 



For the non-botanical reader, some 

 explanation is probably necessary for 

 the proper understanding of the terms 

 used, In the life of every dicotyledo- 



nous plant there is a stage in which the 

 cambium and bast are not arranged in 

 concentric cylinders round the wood, as 

 in the usual Hevea stem. In that stage 

 the stem contains a number of separ- 

 ate longitudinal strands, the vascular 

 buudles, each of which consists of 3 

 longitudinal strands, of wood, cambium, 

 and bast respectively. This is the stage 

 of primary growth. In some plants it 

 persists throughout their whole life, but 

 in the case of Hevea and similar trees 

 another stage soon sets in. The cam- 

 biums of the separate vascular bundles 

 unite into a complete cylinder, and this 

 cylinder proceeds to form wood on its 

 inner side and cortex on its outer side, 

 for the rest of its life. When this 

 happens the stem has reached the stage 

 of secondary growth. It will be under- 

 stood from this that secondary growth 

 has commenced whenever the stem pos- 

 sesses a complete cylinder of wood. 



As far as the cortex is concerned, it is 

 in its primary growth so long as it is 

 green, but when it turns brown second- 

 ary growth has set in. 



It may bp noted in passing that the 

 arrangement of the latex vessels in the 

 stem during " primary growth " differs 

 from that which occurs during " second- 

 ary growth." -In the former stage, the 

 latex vessels may be found between the 

 vascular bundles and in the pith ; but 

 after a complete cylinder of wood has 

 been formed, these inner latex vessels 

 dry up, and subsequently latex vessels 

 occur only in the cortex. This explains 

 Wright's reference (Kegalle, 1906; to a 

 section showing a latex tube in contact 

 with a wood vessel. His slides were 

 sections of seedlings only ; and he was 

 apparently unaware that this contact 

 could only occur in the seedling (if then), 

 for he attaches to it considerable import- 

 ance with regard to the idea of directly 

 feeding the latex tubes by manuring ! 



It is easy for the planter to satisfy 

 himself that secondary growth of the 

 stem sets in when the Hevea plants are 

 only a few weeks old. When they are 

 taken out of the nursery and stumped, 

 all that is living when planted out is 

 " secondary growth " ; the primary wood 

 is buried in the middle of the stem, and 

 the primary cortex (most, if not all) 

 forms the brown layer on the exterior. 

 The new shoots which spring from the 

 stump pass through a stage of primary 

 growth, but practically only in so far as 

 the cortex is concerned. For all prac- 

 tical purposes (since he deals chiefly 

 with the cortex) the planter may reckon 

 that green shoots are in the primary 

 stage of growth, but everything else is 

 in the secondary stage. 



t 



