THE FORM AND FOLIAGE OF THE CONIFERS 365 



drought. Resins and turpentines are also very effective in pro- 

 tecting young conifers from the attacks of parasitic fungi, espe- 

 cially when the trees are wounded. 



Certain pines furnish the resin and turpentine of commerce. 

 Incisions are made through the bark, penetrating the wood. 

 A thick liquid oozes out which is a mixture of resins and oil of 

 turpentine. This liquid is then distilled, driving off the fluid 

 oil of turpentine which is collected. The resin remains behind 



\\ ( - J '^ 



. i 



*s Green \\ 

 I / Tissue \ \ 



/ :' : i 



FIG. 296. Structure of a pine needle (Pinus Laricio) 



The compact green tissue, or mesophyll, with resin ducts <7, surrounds an area con- 

 taining two fibro-vascular bundles, which lie in a peculiar region of transfu- 

 sion tissue t, bounded by the bundle sheath bs. Outside of the green tissue are 

 thick-walled cells forming a rigid tissue r, and around the whole is the heavy 

 epidermis e with lengthwise grooves containing the stomata st 



in the still, and when cool is no longer semi-fluid, but becomes 

 quite hard and brittle. The timber value of certain conifers is 

 much greater than that of most other kinds of trees because the 

 wood is soft, splits regularly, is easily worked, and also because 

 the tree trunks are so straight. The problems of forestry (see 

 Chapter XLI) are largely concerned with the preservation of the 

 pine forests, which are being cut off with little regard to the future. 



