259 



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 

 planting. 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 overhead shade present to discourage the 

 under-growth. 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 neighbours by crowding ; 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 possible, 

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

 be attained quite as fully by setting the rubber trees closer to- 

 gether. 



There is danger, however, that any suggestion which promises 

 earlier returns from rubber culture will be over-done. The rubber 

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

 it would be very poor policy to risk permanent injury from weak 

 spindling growth which overcrowding would undoubtedly cause. 

 More is likely to be lost than gained by trees standing at less 

 than 8 feet for even a few years. Better than uniform .close 

 planting would be to set the north and south rows farther apart 

 than the trees in the rows. With a given number of trees this 

 would secure the maximum of shade on the ground, because the 

 morning and afternoon sun would not shine down the rows. The 

 cleaning of the land or the cultivation of a catch crop or a shade 

 crop between the rows would also be facilitated. The distances 

 would depend on the size which the Castilloa trees were expected 

 to attain in any given locality, the rows from 12 to 20 feet apart, 

 the trees from 8 to 12 feet in the rows being fair average estimates. 



CULTURE. 



"In attempting* to plan a rational culture for Castilloa it will 

 be worse than useless to insist upon all or any of the cultural 

 measures which have been found desirable with coffee, cacao, or 

 other tropical crops. Castilloa is not cultivated for the pods 

 like cocoa, for the flowers like cloves, for the fruits like oranges, 

 nor for the seeds like coffee. The increase of the size of the trunk 

 and of the amount of milk contained in its inner bark are objects 

 of cultural solicitude." 



" Open culture with relatively little cleaning at first would be 

 more practicable if the weeds and undergrowth cut down in the 



* Extvacta iiom Bull. No. 49, Bureau of Plant Industry, U. S. Dept. of AgrJculture. 



