Desaription of the ;Vood 



Sapwood thin, very light yellov^ or nearly white; heart- 

 wood darker. V/ood soft, moderately light, not strong, 

 straight and fairly fine-grained, easily worked, taking a good 

 polish, and not very durable in contact with the soil. Annual 

 rings of growth not clearly marked; the tangential lines of 

 wood ijarenchyma on a smooth transverse surface do not indi- 

 cate limits of growth layers. 



Pores (transverse section) fairly numerous, large (.155 

 mm. in diameter) , round v/hen solitary, usually closed with 

 orange yellovv tyloses, often solitary, but alsc arranged in 

 short radial rows of from Jd to 6 . Vessel walls (longitudinal 

 section) where in contact with ray cells and v/ood parenchyma 

 teear bordered pits v;ith transitions to large simple pits, 

 alv/ays bordered where two vessels are in contact. Perfora- 

 tions simple, circular or elliptical. Vood fibers 1.21 ram. 

 long, v/ith thin walls, large cavities and small, oblique simple 

 pits. .'ood parenchyma highly developed especially around 

 vessels and in the tangential bands clearly visible under the 

 hand lens, xiays niimerous, narrow, from 1 to 4 cells wide and 

 from 4 to 5 times as high. 



Distribution, comaon names and uses 



The name of Central A^nerican rubber trees has been given 



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to several of the species forming the genus Gastilla , on 

 account of their haviiig been for a long time the only source 

 of the rubber exported froa the countries between and inclu- 

 sive IJexico and Panama. Among the ten or less known species 

 of this genus there are at least two which do not produce a 

 eommerc-ial rubber. One of them is the tunu of the Honduras 

 (British and Spanish), the specific distinction of which is 

 not fully known, and the other is the spurious rubber tree 

 of the Isthmus ( Gastilla fnllax C.r'. Cook), which is described 

 here. It was known so far only from the easternmost part of 

 Costa Bica, but the botanical investigations recently made 

 under the supervision cf the Smithsonian Institution have 

 shov/n that it is of more frequent occurrence on the Pacific 

 watershed of Panama, increasing in abundance from Ghiriqui to 

 Darien, where it can be called a common forests tree on 

 fedth sides of the Continental divide. It is because of its 

 restricted distribution on the Isthmus and because it does 

 not i^roduce ruoocr, that it is here designated as Spurious 

 Isthmian rubber tree , the real rubber yielding species being 



