CONTEXTS 



Page. 



Introduction H 



The status of Castilla rubber culture 13 



Castilla versus Hevea 14 



Uncertainties attending rubber culture - 14 



Extent of the Castilla rubber industry 16 



Castilla in the "West Indies 16 



Castilla culture for Porto Rico - - - 17 



Rubber in the Philippines 17 



Botanical study of Castilla - 18 



Difficulties in studying tropical trees 18 



The original description of Castilla 19 



Description and botanical characters 20 



Species and varieties of Castilla 23 



Hooker's monograph of Castilla 23 



Costa Rican species of Castilla 24 



Field notes on Castilla in Guatemala and southern Mexico 25 



Habits of Castilla in the wild state 28 



The rubber tree and the trumpet tree 29 



Castilla not a genuine forest tree 30 



Improvement of rubber trees by selection 31 



Problems presented by the latex, or ' ' milk " 32 



Evolutionary arguments regarding latex 33 



Functions ascribed to latex 34 



The structure of latex 35 



Seasonal influences on latex 36 



Latex in desert plants - 37 



Water storing as a function of latex 38 



Significance of multiple tapping 39 



Climate and rubber production 39 



A continuously humid climate not necessary for Castilla 39 



Greater abundance of Castilla on the drier Pacific slope 40 



Freer flow of milk in drier regions 40 



Decrease of milk with altitude and continuous humidity 41 



Castilla in Nicaragua '. 43 



Castilla in Costa Rica 43 



Castilla on the Isthmus of Panama 44 



Analogy of the Assam rubber tree 45 



The Para rubber tree in humid localities 45 



Productiveness of Para rubber trees in dry situations 46 



The true climate of Hevea 17 



