92 RESINOUS SECRETIONS. 



a close investigation shows that it is connected with exudation into 

 an intercellular space, or caused by the drying up of the outer layers. 



With the conversion of the sap- into heart-wood, the resin-canals are 

 filled up by tyloses,* so that a subsequent flow of resin from the sap- 

 to the heart-wood or vice versa is impossible.! 



The quantity of turpentine secreted depends much on the greater 

 or less development of the summer wood in or near which most of 

 the resin-ducts are found ; it is also greatly influenced by the heat 

 or moisture of the climate, the former acting as a stimulant, the 

 latter as a check to the secretion. The quality varies with the age 

 and vigour of the tree, the humidity of the atmosphere and the 

 season in which it is collected. 



The Pines in the Mediterranean region, and especially the plantations 



of Pinus Pinaster in the south of France, supply turpentine in greater 



quantity and of better quality than that obtained further north, while 



the Pine forests of Sweden and Xorway supply only the coarser 



products as tar and pitch. The turpentine of American commerce is 



procured chiefly from the extensive " Pine Barrens " of the South 



Eastern States, where, during the great heats of summer, it flows from 



the trees so copiously as to require but a comparatively small amount 



of labour to obtain it. In the great pine woods of Canada it would 



not at present repay the cost of collecting for exportation, in consequence 



of the cheaper rate at which it is procured further south. The Coniferse 



of the Himalaya yield but a small amount of resinous products owing 



to the humidity of the climate, with the exception of Pinus lonyifolia 



which is spread chiefly through the outer or tropical range between 



1,500 and 6,000 feet elevation, where the greater heat more than 



counteracts the excessive humidity. And in Britain 'although the more 



equable temperature of -summer and winter, especially in the districts 



of the greatest rainfall, is favourable to the rapid growth of the trees 



the resinous products are not sufficiently abundant to be worth collecting'. 



The crude turpentine consists of two principal ingredients, a volatile 



oil commercially known as Oil of Turpentine, and Colophony the 



crystallised resin, which can be separated by distillation. Oil of 



turpentine, a hydron-carbon having for its chemical formula Ci H i6 



in its pure state is a colourless liquid of powerful odour, almost 



insoluble in water but dissolving in alcohol or ether and absorbing 



oxygen rapidly from the air, especially when mixed with ceruse or 



white-lead ; it dissolves sulphur and is a good solvent for grease. 



It is also a powerful solvent for resins which form the bases of 



most varnishes,, and from its great volubility, it quickly flies off or 



dries away, leaving a thin coat of the varnishing substance on the 



surface to which it has been applied. It is the only known volatile 



oil that mixes readily with paint without affecting its properties, 



diluting it so that it may flow freely from the painter's brush, causing 



* For explanation of these processes see Sack's Text Book of Botany," Vines' Trans- 

 lation, p. 24. 



t Ex Gardeners' Chronicle, XIV. s. 3 (1893), p. 327. 



