54 CENTRAL AMERICAN RUBBER TREE. 



LEGUMINOUS SHADE TREES TO BE PREFERRED. 



Where the policy of thinning- out the forest is followed the question 

 arises as to which trees are to be left and which cut down. A study 

 of coffee and cacao culture has revealed the probability that much of 

 the benefit ascribed to shade is due in reality to the nitrogen furnished 

 by the bacteria of the root tubercles of the leguminous trees which 

 are preferred in all countries where the shade culture of coffee has 

 become popular. If shade trees are to be planted with rubber, they 

 must be different from the species of Inga which are preferred for 

 coffee shade in Mexico and Central America, for the reason that Cas- 

 tilla grows faster than Inga. Some leguminous trees, however, grow 

 with great rapidity and may be able to outstrip the rubber, ^so com- 

 parative experiments seem to have been made. If. as suggested 

 above, shade trees are more useful as windbreaks than for the shadow 

 they cast on the rubber, the planting of fruit trees like the mango or 

 other useful species in rows or hedges would be preferable to scatter- 

 ing them amongst the rubber. 



DISTANCE BETWEEX TREES. 



As yet there have been no experiments yielding any definite infor- 

 mation on the above point, but the recent trend of opinion among 

 planters seems to be distinctly in the direction of closer planting. 

 There has been a gradual decline from 20 feet and upward between 

 trees to 12 feet and under. 



The questions of shade and of distance between trees are closely 

 related and need to be considered together because several of the 

 arguments for shade can be met. wholly or partially, by close plant- 

 ing. The first of these is that of the greater expense incidental to 

 open culture. The frequency with which the land requires to be 

 cleaned and the period of years during which it would be necessary 

 to continue such cleaning depends largely upon the amount of over- 

 head shade present to discourage the undergrowth. Some planters 

 on the Isthmus of Tehuantepec are evidently taking advantage of this 

 fact and are setting close, with the intention of removing alternate 

 trees before they are large enough to injure their neighbors by crowd- 

 ing: and it is expected that if they are "tapped to death" they can 

 be made to yield enough rubber to more than cover the expense of 

 planting. At least there seems to be no reason why. if the land is to 

 be cleared, it should not be made to produce as much rubber as possi- 

 ble instead of being planted with useless trees for a purpose which 

 can be attained quite as fully by setting the rubber trees closer 

 together. 



There is danger, however, that any suggestion which promises 

 earlier returns from rubber culture will be overdone. The rubber of 

 very young trees is of low grade and expensive to collect; also it 



