POISONS OF VEGETABLE OniGIN 211 



having a flattened form ; the kimen is usually small. 

 The primary walls of the fibres are hgnified and some- 

 times yellowish, while the thickening-layer or later- 

 formed ^rt of the wall consists of cellulose, and occa- 

 sionally contracts away from the primary wall. The 

 wood (xylem) includes a large proportion of parenchy- 

 matous tissue, and therefore the medullary rays are not 

 very conspicuous in a transverse section. Starch is 

 present in some of the parenchymatous tissue (of the 

 wood-parenchyma and of the medullary rays). 



" Numerous groups of fibres occur in the wood- 

 parenchyma, and are precisely similar to those found 

 in the bast. The wood-vessels occur singly and in rows 

 or groups of two, three or more, the isolated vessels 

 being usually elliptical, and the largest of them reaching 

 nearly 0-2 mm. in diameter. Some of the parenchy- 

 matous tissue of the wood is lignified, especially in 

 patches enclosing one or more groups of vessels. Pith 

 is not present in the specimens examined." 



D, elliptica gi'ows readily in the Straits Settlements ; 

 the roots are sold in two grades on the market. There 

 is a good local demand for them done up in bundles for 

 sale by weight in native shops. It would seem that 

 they are frequently adulterated by the substitution of 

 other roots. The Director of the Botanic Gardens, 

 Singapore, prosecuted a Chinese in 1918 for causing 

 damage to a ficus tree in the garden ; the accused 

 pleaded in court that he was taking the aerial roots as a 

 medicine. A fortnight later he came back with an 

 accomplice and a cart and carried away a further 

 quantity for the adulteration of tuba roots. The detec- 

 tion of spurious tuba roots is of considerable economic 

 importance ; it will be seen later that only two kinds 

 (D, elHptica and D. uhginosa) have been proved to be 

 useful for insecticidal purposes. Three samples of 



