Gums, Resins, 



128 



BLACK WATER. 



Latex which is quickly gathered and quickly corked up away from the air 

 forms no black water. Black water gets blacker from longer standing in the air 

 until about five days after gathering. Fresh black water can immediately be 

 turned to its deepest black by ammonia, but ammonia will not affect black water 

 five days old. I believe that the action of ammonia is the same as the oxidation 

 in the air. Contact with metals will make black water blacker. Sugar slowly 

 takes the black colour away, and latex which has been allowed to oxidise has water 

 which resembles that formed by sugar. I believe that sugar reduces it to its 

 former state. I do not see auy reason to think that rubber itself is an oxidation 

 product ; it is possible, but if so, it can be further oxidised by the use of nitric acid. 



YIELD OP CASTILLOA. 



I believe that accounts of the yield of the Caslilloa tree have been greatly 

 exaggerated, either by intention or by mistake. Great care must be taken in trying 

 to estimate the yield. Natives will not count half the trees they tap, and in that 

 case the yield will appear to be more than double what it really is. Here, owing to 

 poor soil, wrong methods of tapping etc., the trees are irregular in their growth. It 

 does not pay to tap only big trees, and the little ones bring down the average. The 

 average yield for trees eighteen or twenty inches in circumference should be 

 between one and two ounces per tapping. I think it would be safe to calculate on 

 half-a-pound a year from good six year old trees. 



In calculating yields it makes a difference whether the rubber is weighed 

 immediately, or after drying some time. Rubber made wet by coagulation and 

 apparently dry will lose sometimes as imich as 20 per cent of its weight in the first 

 day's drying. What the trees will yield in the future cannot be definitely deter- 

 mined. Two wild trees gave between one and two pounds each to a tapping, using 

 ladders. These trees were both a few inches over three feet in circumference. At 

 the present rate of growth the tree should reach that size when about fifteen years 

 old. It is probable that the wild trees were older, as they were growing in the shade 

 until the land was cleared. 



THE OCCURRENCE OP RESIN IN YOUNG TREES, AND GROWING PARTS OP TREES. 



Experiments of others have shown that young trees and younger parts of 

 old trees contain a large percentage of resin in their rubber. I have made one obser- 

 vation which suggests a reason for this. In cutting a temporary branch of leafy 

 stem it is noticeable that the latex comes very close to the outside bark, and that 

 there appears to be a second ring of tubes, in the inner bark. Microscopic examina- 

 tion of these parts shows a large number of collenchyma cells close to the outside 

 bark. These cells are similar to bast fibres, but the thick part of the walls is not 

 uniform. Collenchyma cells are never formed by older trees except in their young 

 parts. I think it possible that these collenchyma cells carry latex which is richer 

 in resins than ordinary latex, and which may possibly be entirely resin.* Of course 

 these collenchyma cells remain in the plant as it grows older, but form a very small 

 proportion of its tissue at that time. It is possible that rubber or resin may have 

 some chemical relation to the cellulose of which the thick walls of both collenchyma 

 and bast fibres are formed. 



CASTILLOA VERSCS HEVEA. 



The Para rubber tree shows some important differences in its latex from the 

 Castilloa. Of course, all that I have noted in this tree is done here in Nicaragua, and 

 it may behave differently in Brazil or Ceylon. 



* Collenchymatous cells contain neither latex nor resin. 



