GRASS OF ECONOMIC PLANTS. 199 



sively cultivated in Upper India ; the fibre is used for making 

 ropes and sail-cloths. 



Grass Gum Trees, a name applied to the different species of 

 Xanthorrhoea, a genus of the Lily family (Liliaceae). This re- 

 markable genus consists of nine or ten species, natives of 

 Australia. Stems cylindrical, formed by the closely -packed, 

 broad bases of grass-like leaves, and attaining a foot or more in 

 diameter. X. arhorea and X. quadrangularis attain a height 

 of 6 to 10 feet, and the flower-stem springs like a stout rod from 

 the centre of the crown of leaves, and frequently is 10 to 20 

 feet long, the upper part being densely covered with small 

 yellowish -white flowers. The leaves are often burnt by the 

 grass fires, leaving the blackened stems standing, w^hich, at a 

 distance, have the appearance of black men, from wliich circum- 

 stance the name Black Boy Trees has been applied to them. 

 The smaller species look like thatched beehives. They yield a 

 fragrant resin of two kinds, called Black Boy, or Botany Bay 

 Gum, and Gum Acaroides. This last yields Picric acid when 

 treated with Nitric acid, and is extensively used in the pre- 

 paration of the highly explosive compound Picrate of Potassium. 

 This acid is used for dyeing silk and wool, and imparts to them 

 a yellow colour. The gum-resin is sometimes made into candles. 

 These plants are of very slow growth, requiring many years 

 before they form a stem, as shown by an example of a plant at 

 Kew thirty years old, and still stemless. 



Grass Tree [Kingia aiistralis), a remarkable plant of the 

 Eush family (Juncacese), native of South and South -West 

 Australia, growing in dry places. It has a trunk a foot in 

 diameter, composed of the bases of the hard, three-sided grass- 

 like leaves. The leaves are successively produced from the top 

 of the stem, and curve downwards. The older ones fall away, 

 or more often are burnt away by the grass fires, leaving the 

 charred and blackened stems, which in old plants attain a 

 height of 6 to 8 feet. The flowers are small, borne in dense 

 round heads on a foot-stalk about a foot long, several rising 

 from the crown of leaves. 



