i6 



of the hairs of the lower surface as a protection against excessive 

 transpiration. The leaves suffer when they are obliged to part 

 with more water than they can obtain, and their falling off is then 

 an advantage because it decreases the demand for water. Thus, 

 although Castilloa is not a desert plant, the falling of its leaves 

 in the dry season is the same physiological phenomenon which 

 appears so conspicuously in deserts, viz., the loss of the leaves as 

 a protection against drought. Many desert plants such as 

 Parkinsonia, Fouquieria, Peireskia, and species of Euphorbia put 

 out leaves for the wet season only, while most of the Cactace^ 

 and many Euphorbias have discarded leaves entirely and expose 

 as little surface as possible to the air. 



This digression may help to make it apparent that the planter 

 who desires to give intelligent consideration to the agricultural 

 question of shade should dismiss the notion that the rubber tree 

 derives a direct advantage from standing in the shadow of another 

 tree , on the contrary, it is probable that interference with the 

 sunlight is always a direct disadvantage. Shade, if used at all, is to 

 be applied and justified on the ground that it will preserve the 

 moisture of the soil or of the atmosphere or serve some other cul- 

 tural purpose. By conserving the soil moisture, clean culture may 

 produce some of the desirable effects commonly ascribed to shade. 

 Open culture may be, and probably is, less advisable than either 

 clean culture or a moderate shade culture. 



Open culture with relatively little cleaning at first would be 

 more practicable if the weeds and undergrowth cut down in the 

 dry season could be left spread over the ground. This would do 

 more to conserve the moisture of the soil than the same vegetation 

 alive, but the danger of fire will in moist localities forbid the use 

 of this method of culture. 



If the present question could be settled by deciding whether or 

 not Castilloa needs to be protected from the sun, it would be easy 

 to establish the negative view ; but with shade recognized as a 

 means of influencing natural conditions of soil or climate it be- 

 comes evident that each planterwill need to use his best judgment in 

 determining what local conditions require. In Costa Rica, Koschny 

 advises the thinning of the forest by the removal of two or three 

 trees out of every five. At La Zacualpa more are cut out. 

 Some of the planters on the Isthmus of Tehuantepec practice clean 

 culture. No general principles will determine which is best, 

 because no one method is applicable everywhere. 



RELATIVE COST OF SHADE CULTURE. 



It must be remembered, in addition, that the planter finds him- 

 self compelled to decide not what will be the best for the rubber 

 trees, but what is the best he can afford to do for them. Is it, for 

 example, good policy to use labour and capital in keeping a tract 

 of planted land clean, or will more be gained ultimately if one 

 contents himself with somewhat slower growth and improves 

 the opportunity of planting additional tracts with trees that can 



