•May, 1910.] 



389 



Saps and Exudations. 



is making a sensation unparalleled in the 

 history of tropical agriculture. This is 

 wholly due to the advantage taken of 

 the wound-response, which appears 

 totally absent in Castilloa. The one 

 gives pounds of rubber per annum, 

 whilst the other gives ounces. 



The latest accounts* of Castilloa in 

 Mexico are not over-encouraging, but 

 with rubber at anything like its present 

 price, the estates now coming into bear- 

 ing will doubtless prove remunerative. A 

 six-year-old Castilloa apparently gives 

 only 2 to 3 oz. of rubber in the year 

 without seriously injuring the tree, 

 whereas a Hevea of similar age will yield 

 about a pound. At ten years old the 

 proportion appears to be about 4 or 5 oz. 

 tor Castilloa and 3 to 4 lb. for Hevea. 

 It seems that the more Castilloa has 

 been studied from the economic stand- 

 point, the less satisfactory it becomes, 

 while, ou the contrary, Hevea has ever 

 continued to grow in favour. 



This phenomenon of wound-response 

 in Hevea is not only of great practical 

 importance in rubber cultivation, but is 

 also of considerable botanical interest; 

 and requires more extended investiga- 

 tion. To what circumstances is the in- 

 creased flow of latex arising from injury 

 due ? In Hevea the milk (laticiferous) 

 tubes reside chiefly in the innermost 

 third of the bark, i.e., in the youngest 

 and most functional patt of the bast 

 (phloem.) New tubes are continually 

 being formed in the fresh phloem, pro- 

 duced by the actively dividing layer of 

 cells, the cambium ; these take the place 

 of the older exterior tubes, which be- 

 come compressed and eventually ob- 

 literated by the tree's expansion. It 

 the laticiferous tubes in a definite area 

 of bark were completely drained of their 

 contents, two possibilities might happen. 

 On the one hand this region might yield 

 little or no latex, until the cambium 

 formed new tubes — a process occupy- 

 ing some time ; or, on the other 

 hand, latex from the adjoining areas 

 might flow in and refill the drained 

 tubes, so that on retapping in a day or 

 two an abundance of latex would exude. 

 The first possibility may represent the 

 behaviour of Castilloa, the second that 

 of Hevea. In the latter tree the time 

 would appear to be too short for any of 

 the increased flow to be accounted for 

 by the formation of new laticiferous 

 elements. Probably in this case an in- 

 jury causes an inrush of water into the 



* India. Rubber Journal, 1909, Vol. xxxvii, 

 p. 701. An article on Castilloa cultivation in 

 the Quartor-contury No. (p. 85) of this Journal 

 gives higher yields, viz., about half thoso of 

 Hevea. 



surrounding intact tubes, and perhaps 

 also into the severed ones, which will 

 be now plugged by hardened latex. 

 This flow of liquid towards the injured 

 spot may be required for the reparation 

 of the wound. 



The latex which oozes out from a 

 primary tapping of a Hevea tree is 

 thicker, containing less water and more 

 caoutchouc than that which flows from 

 subsequent tappings; and further, it 

 appears to give a poorer quality of 

 rubber. In practice it is a disadvantage 

 to have latex of a treacly consistency 

 exuding, as much of it is apt to harden 

 ou the tree before it leaches the re- 

 ceptacle, producing inferior scrap rubber. 

 In fact, the initial tapping is of little 

 value from a rubber-yielding poiut of 

 view ; it only serves as the guide to 

 future work. Sometimes drip-tins are 

 fixed just above the tapping area. These 

 allow water to drop slowly upon the 

 incisions and so prevent the latex in its 

 course down the trunk from drying on 

 the tree. A little ammonia or formalin 

 added to the water makes this device 

 more effectual, as the coagulation of the 

 latex is prevented by these reagents. 



The latex from the second tapping is 

 thus thinner and more copious, and it 

 continues so far for many subsequent 

 tappings. The percentage of caoutchouc 

 in the latex resulting from this multiple 

 tapping has, however, never been ade- 

 quately worked out. Presumably the 

 percentage (roughly 30 to 40) is fairly 

 uniformly maintained for quite a long 

 period (three to four months), but 

 eventually falls, and a thin watery latex 

 results, which does not pay to collect. 

 This indicates that the tree requires 

 a rest. 



Wound-response appears to be a peculi- 

 arity of Hevea alone, or to speak more 

 guardedly, it has not been shown to 

 occur, as yet, in any other rubber tree 

 to the extent that advantage may be 

 taken of it in practice. It may exist in 

 a much less marked degree, but this 

 remains to be demonstrated. 



Considering that the laticiferous sys- 

 tem of Castilloa is of an essentially 

 different construction from that of 

 Hevea, At is perhaps not altogether 

 remarkable that the two trees behave 

 differently when tapped. In the former 

 the laticiferous tubes are in mutual 

 connection from the beginning. Special 

 cells are differentiated in the embryo, 

 and these produce by growth in length 

 and ramification the whole laticiferous 

 system of the plant. This is known as 

 the non-articulate system. 



