52 CENTRAL AMERICAN RUBBER TREE. 



in proportion to leafage is a sign of unfavorable conditions or of bad 

 plantation management. It does not follow, however, as some have 

 seemed to suppose, that forest shade is necessary to grow long-trunked 

 trees. In coffee culture it is plain that the most wood is formed not 

 by shade culture, but by planting close in the open, and the older- 

 planted trees of Castilla at La Zacualpa, if not as slender and as smooth- 

 trunked as those of the forest, are certainly tall and slender enough to 

 furnish ample evidence that open culture does not cause a low, spread- 

 ing growth, if the trees stand close enough together (PI. I). The 

 Zacualpa experiment is of further significance in this connection, 

 because it shows that a harmful degree of crowding was by no means 

 reached. In numerous instances where from three to five (PL XII) 

 trees grew in a cluster their trunks were each equal in size to those of 

 many of their neighbors which stood alone. a 



Coffee trees which stand too close together lose the use of their lower 

 branches, which become interlaced and shade one another, and ulti- 

 mately only the top of each tree continues to grow and produce fruit. 

 The planter must choose a middle course between the injury of his 

 bearing trees by crowding and the waste of capital and labor in keep- 

 ing clean unused land between trees planted too far apart. With the 

 rubber tree the seed is a consideration entirely secondary to the growth 

 of the trunk. In comparison with coffee it may be said that the crowd- 

 ing of rubber trees is desirable, and that it finds its limit, not in the 

 discouragement of lateral branches, nor even in the lessening of 

 the size of the individual trees, but in the decrease in the amount of 

 rubber which can be produced on a given area of land. 



SHADE AND RUBBER PRODUCTION. 



The general question of shade can not, however, be treated as closed 

 until its influence on the }deld of rubber has been tested by careful 

 experiment. From the facts given on previous pages it appears very 

 improbable that less rubber will be formed in the open than under 

 shade; the difficulty, if any, is likely to arise in connection with the 

 extraction of the rubber. The desirability of tall trunks to afford a 

 large tapping surface has been noted already, but there may be other 

 disturbing factors. The pressure of the liquids inside a tall columnar 

 trunk may be greater than if it were thicker and shorter, so that more 

 milk would be forced out on tapping. The bark of trees more exposed 

 to wind and sunlight becomes thicker and there may be differences in 

 texture which would affect the flow of milk. The air is much drier 

 outside than inside the forest, and this might soon impede the flow of 

 milk, though this suggestion seems to be negatived by the fact that 



« Planting in clusters might be advisable on some accounts, since the trees' would 

 better shade their trunks and the ground under them, but the difficulty of properly- 

 tapping such trees would seem to exclude this method of culture. 



