Gymnosperms : Coniferae Pinus as Timber-tree. IV. 



PINUS SYLVESTRIS, characteristic 'Hard Pine' of N. Europe, imported 

 since fifteenth cent, from Baltic ports, as 'Yellow' and ' Red Deal' ('White Deal' 

 = Spruce). Variable in texture according to mode of growth. Finest trunks 

 floated down Vistula to Dantzic ; poorer quality from Sweden and Norway, used for 

 building-construction, as in planks. Dry material gives details of dead xylem- 

 tracheides and rays : parenchyma poorly expressed : softened by soaking in water, 

 and coloured by phloroglucin-reaction. 



I. Naked-eye characters : note width of annual rings, 1-3 mm. (max. 7-8), 

 marked by dark zone of summer wood ( mm.) : lighter specks as resin-duct islands, 

 scattered irregularly ; M. Rays as fine lines, the broader rays alone visible to the eye. 



II. Transv. Sect. : All tissues tend to increase in dimensions in older trees, up 

 to a maximum of about 30-40 ft. high, as compared with small growths and buds of 

 branches. An annual ring of 3 mm. shows radial series of 50-80 pitted tracheides, 

 and the spring-tracheides may be 50-60 ll in radial depth. Medullary rays 6-8 

 per mm., and 2-18 rows apart (average 5-6). Demarcation of annual ring very 

 clear; the thickening of the summer tracheides up to 6 /x wide, on a very definite 

 intermediate primary wall. 



III. Longit. Had. Sect. : Note great size of pitted tracheides, up to over 

 4 mm. long, and 30-60 jx wide, with bordered pits 20 jx or more in diam. (inner circle 

 6 fi) often closely set; exceptionally 2-ranked in spring wood: spiral striation of 

 wall-lining, and oblique pits of summer wood flared along the spiral path. 



M.R.P. as before, broadly oval pits, 1 per tracheide, extending to 40 \x wide 

 radially ; occasionally 2 per tracheide. 



M.R.T. may be 3-4 deep in one ray; jagging very steep, and irregularly 

 toothed; bordered pits 10 /x diam., also in transverse and oblique end-walls. 



IV. Longit. Tangent. Sect. : In the largest tracheides of the spring wood bor- 

 dered pits should be cut well enough to show the torus. Note distinction of uniseriate 

 and fusiform rays, the former rarely more than 15 cells deep (300 fx). M.R.P. and 

 M.R.T. distinguished by contents and wall-structure. 



Alburnum and Duramen : The newly formed tissues are used for conduction 

 of the transpiration current ; older tracheides become full of air-bubbles : but so long 

 as the parenchymatous units are alive, the xylem is so far ' sap-wood ', and water may 

 be stored in it, or the parenchyma used for storage of reserves as starch. As the 

 living cells die off their contents are lost ; excretions only remain, and these undergo 

 chemical decomposition, infiltrating the walls, as tannins, resins, &c, differentiating 

 Duramen or ' Heart- wood ' in colour, texture, and general properties. The 

 alburnum of Pinus is pale yellow, and the duramen pale reddish, hence commercial 

 names. The boundary of the duramen is not exact to the ring-pattern : the 

 differentiation is but slight, and gives no special reaction with reagents. 



Knots : As the upper growth of the tree shades the lower laterals, these die ; 

 not being definitely cut off by an absciss-layer they remain to decay in situ, leaving 

 dead snags of smaller or larger size. In the course of time the bases are imbedded in 

 the advancing rings, and buried in the wood. In Pinus such laterals, in advanced 

 condition of chemical decomposition, beyond the duramen-condition, broken off 

 short, and covered by healing layers of new wood, are seen projecting obliquely 

 and radially through the timber. Sections of these constitute ' knots ' ; two forms 

 may be distinguished : e. g., in Pinus, a branch may die at 40 years old, as seen by 

 checking approximate number of rings in transverse section of the knot, leaving 

 a broken snag on the trunk. The wood of the basal part of the branch is continuous 

 with that of 40 year's growth of timber, being close-grained with reduced growth-activity, 

 and duramen in texture. At the base of the snag, cambium may still continue to 

 follow on for many years (10-20), and the timber gradually encloses the base of the 

 lateral, conformably as before. 



The exposed dead wood of the snag undergoes extreme chemical decompostion, 

 becoming resinous and infiltrated to a translucent mass, in which even the walls may 

 become more or less dissolved. This part, as it is gradually imbedded in successive 

 annual rings, is non-conformable with the advancing timber and fills a cavity the 

 interspace being sealed with resin. Sections in a plank give ' loose knots '. 



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