TROPICAL AGRICULTURAL METHODS 25 



to have best results from permanent partial shade furnished by 

 ceara rubber or other shade trees in the plantations. 



In exposed localities windbreaks seem to be perhaps more 

 urgently needed in the Tropics than in temperate climates. 

 Tropical plants are extremely sensitive to change of tempera- 

 ture, especially to relatively^ low temperature. The constant 

 blowing of the dry trade wind causes rapid transpiration of 

 plants and a consequent lowering of the temperature of the 

 plants. Rows of trees planted for the purpose of furnishing 

 windbreaks are therefore of great benefit when running at 

 intervals of lOO to 200 yards across the fields at right angles 

 to the prevailing wind. In fields thus furnished with wind- 

 breaks many tropical crops show a regular gradation in size 

 from the lee side of each row of windbreak trees to the wind- 

 ward side of the next row of trees. Some crops in the most 

 exposed situation do not attain a size greater than half that 

 of the plants in the lee of an effective windbreak. 



The choice of a plant for windbreak purposes depends some- 

 what on the nature of the crop to be protected and the strength 

 of the winds. For low growing plants, pigeon pea furnishes 

 an excellent protection against the wind. This may be grown 

 in dense rows and pruned back annually so as to form a close 

 hedge somewhat resembling the privet hedge in appearance. 

 The pigeon pea is a perennial and may best be used as a wind- 

 break in gardens and for the protection of truck crops under 

 field conditions. The castor bean grows rapidly and is an 

 excellent plant for withstanding fierce and continuous winds 

 in exposed localities. It will continue to grow rather rapidly 

 even when the winds are so strong as to prevent the develop- 

 ment of a symmetrical bush. 



In exposed localities in the immediate neighborhood of the 

 seashore, the Majagua or hau (Hibiscus tiliaceus) is an excel- 

 lent shrub for use as a windbreak. It will thrive with its feet 

 in salt water and is not destroyed by salt spray, the foliage 

 being promptly restored after burning by the salt water. The 



