222 THE CENTRAL AI^IERICAN RUBBER TREE 



good results in many cases, but the average yield per tree 

 obtained on tapping large plantations has been small. 



Mexico. — On the La Zacualpa No. 1 plantation about 

 400,000 trees, varying from four to twenty years old and 

 including some scattered wild trees, have been tapped 

 during recent years. The tapping has been done three 

 times during the year, and the average yield of rubber 

 from all the trees has been about 4 oz. per annum. 

 Formerly the trees were not tapped until they were 

 seven years old, and the average yield per tree was then 

 between 7 and 8 oz. per annum. Several thousand 

 twenty-year-old trees occur on the estate, and these 

 have furnished an average annual yield of 2 J lb. of rubber. 

 The variety of tree cultivated at La Zacualpa is Castilloa 

 lactifiua, which is one of the best rubber-yielding species. 

 The following results of single tappings of trees on 

 estates in Mexico have been given by Smith : 



Pittier has recorded the opinion that the yields of rubber 

 from cultivated Castilloa trees in Mexico were formerly 

 much exaggerated. He states that trees which yield 500 

 grams (Tl lb.) of rubber at one tapping are not uncommon, 

 but that the number which only yield 50 grams is legion. 



Panama. — In 1892 Weber conducted a series of experi- 

 ments on Castilloa trees growing at the Las Cascadas 

 plantation on the Isthmus of Panama in order to deter- 

 mine the yield of rubber. His results are summarised in 

 the following table : 



