ADVANTAGES OF CLEAN CULTURE. 49 



most favorable to its growth in nature; these are more nearly attained 

 when the forest is thinned out or partly cut away. 



Koschny, who distinguishes four kinds of Castilla in Costa Rica, 

 says that the "hule bianco." or white Castilla, is the only one adapted 

 for cultivation, and that this is never found in the deep forest, but 

 in more open places, where the foliage has access to the sunlight. 



Experiments with forest planting were studied in eastern Guate- 

 mala and in southern Mexico, and in both instances the young trees 

 were at an obvious disadvantage in comparison with others planted 

 at the same time in more open situations. Plates XIII and XIV 

 will serve to illustrate the difference, for although the tree shown 

 in the latter had suffered the loss of its terminal bud the number of 

 leaves and the amount of new growth it had made was not below 

 the average. Many individuals had hardly grown at all in six months 

 and many had died. On the other hand, it should be explained that 

 the trees, like that shown in Plate XIII, while they had no shade 

 overhead were not exposed to the extent which might be implied by 

 the term "'open culture." since they stood in a clearing only a few 

 acres in extent. The neighboring forest gave shade in the morning 

 and afternoon, and the atmosphere was undoubtedly kept far more 

 humid throughout the day than would be the case in a large tract of 

 unshaded land baked by the tropical sun. They were also undoubt- 

 edly assisted by a mulch of dead leaves and brush. Trees 12 feet high 

 were said to be only 1 year old. 



It would seem, then, that one of the extreme suggestions — the plant- 

 ing of rubber in the undisturbed forest — is clearly inadvisable and 

 may be dismissed from further consideration. The other extreme — 

 clean culture — is not so readily condemned as impracticable, since 

 observations in southerr Mexico establish the fact that even single 

 trees, standing in the open sun and with little other vegetation near 

 them, are not only able to survive six months of dry weather, but 

 actually remain more leafy at the end of the dry season and thus 

 appear to suffer less from drought than those on land covered with 

 weeds and bushes. The reason for this apparent anomaly may not be 

 difficult to conjecture, since it is plain that a tree standing in cleared 

 ground has a monopoly of all the moisture which rises in the soil, 

 and may thus have a distinct advantage over one obliged to share 

 a similar supply of water with a tangled mass of other plants which 

 expose to the atmosphere a total leaf surface many times that of 

 the } T oung rubber tree. Moreover, it is also clear that the water 

 required to supply the needs of this large amount of vegetation would 

 greatly exceed that which escaped from the exposed surface of the 

 soil. It is even doubtful whether a covering of low vegetation greatly 

 checks the evaporation from the soil; it may be as great or greater 



4870— No. 49— 03 4 



