RESINOUS SECRETIONS. 91 



that liave been notched and mutilated for their resinous secretions, is 

 often so full of resin that it can be used as torches in the place of 

 candles in huts and even in mines. Lamp-black used in the manu- 

 facture of printer's ink is obtained in the south-west of France by 

 burning the roots and stumps of Pinus Pinaster in closed masonry 

 chambers. And in all parts of the world where coniferous trees 

 abound, especially throughout the sub-arctic regions of Europe, Asia and 

 Xorth America, the wood when not used for constructive purposes is 

 the chief and often the sole source of fuel for the inhabitants. 



Bark. The 1 bark of Tsuf/a canadensis is rich in tannin and it is 

 the principal material used in the eastern provinces of the Dominion 

 and the northern United States for tanning leather. The bark of 

 Pinus longifolia is similarly used in northern India, and that of 

 Dacrydium cupressinum in Xew Zealand. And along the inner and 

 higher Himalaya the bark of Abies WeNriana is often used for 

 roofing shepherds' huts. 



RESINOUS SECRETIONS. 



IN the description of the anatomical structure of coniferous wood 

 given in the preceding pages, mention is made of " resin-ducts" or 

 intercellular passages in which turpentine is secreted. These " resin- 

 ducts " are widely distributed throughout the CONIFERS, but in the 

 TAXACE.E they are either altogether absent as in Tax us, or they are 

 confined to certain organs only as in Torreya and Dacrydium. In 

 the CONIFERS, more especially in the Fir and Pine tribe (Abietineae), 

 they are found in all the organs, root, stem, pith, medullary rays, 

 bark, leaves, etc., always following the direction in length of the 

 organ in which they occur, but often branching ; they are thence 

 visible in transverse sections, in the leaves as shown in pages 33 35, 

 and in the young stein as shown in Fig. 44, page 83. From recent 

 investigations into the origin and properties of resin by Dr. Heinrich 

 Mayr of Munich, we learn the following interesting facts : 



( hily in an invisible molecular form in the protoplasm can existing 

 resin pass into an intercellular space, so that the cell-wall is only 

 permeable for resin so long as it is in process of formation. A 

 secretion of resin in the canals or " ducts " can only occur during the 

 first year or two of the formation of the annual rings. 



Finished cell-walls, whether lignified, thickened or not, cannot be 

 permeated by resin so long as the respective walls are saturated with 

 water, and as in the living tree both sap- and heart-wood are always 

 saturated, it follows that all cell-walls of normal wood in the living- 

 tree are always free from resin. 



All resin-holding spaces are surrounded by an impervious, continuous 

 cell-tissue, and are therefore completely isolated. The resin cavities are 

 entirely closed on all sides, and never open at the exterior in an un- 

 injured tree. 



There is no spontaneous exudation of resin towards the surface ; 

 every outflow of resin is pathological ; where prirno aspedu a spontaneous 

 outflow appears to occur, as on the buds and cones of different Conifers, 



