Vol. VIIJ. No. 197. 



THE AGRICULTURAL NEWS. 



3.57 



THE RELATION OF THE SAWING AND 

 USE OF TIMBER TO ROTS. 

 The following extracts are taken from Bulletin 

 No. 6 of the Division of Pathology and Physiology of 

 the Hawaiian Planters' Association. They show how 

 the tendency of wood to be attacked by fungi has 

 a relation to its power of absorbing water, and how this 

 .property depends on the way in which it is cut. 

 Investigations were made in conne.xion with the travel 

 of the water in three directions: (1) along the grain 

 ■(longitudinally), (2) along a line extending from the 

 ■centre to the circumference (radially), (3) in a direction 

 at right angles to this (tangentially). 



The relative action of the timber rots on a piece of 

 timber is partly a function of the internal moisture of the 

 timber; and the advent and residence of moisture in the 

 timber, are functions of the structure. A few examples will 

 illustrate this. 



It will be noticed that shingles sawn radially, or nearly 

 .so, last longer than those that are sawn tangentially. The 

 reason for this is apparently that these shingles dry out more 

 evenly and quickly, so that they are less liable to warp and 

 ■ crack. The tangential shingles keep the moisture underneath 

 from evaporating, so that while their upper surface is nearly 

 dry, and hence shrunken, the lower surface is still wet and 

 expanded or swollen. On the other hand, in a shower of 

 short duration, the tops of tangential shingles become wet and 

 expand, while the lower s-urfaces are still comparatively dry, 

 so that here, again, they warp or curl. In the cour.se of time, 

 this mechanical action works changes in the wood, and it 

 will be found that such shingles crack and rot away fastest. 

 On the other hand, shingles sawn radially get wet and dry 

 evenly and c[uickly, with least tendency to crack. This 

 cracking is a matter that is largely mechanical, and, of course, 

 must not be confounded with the direct action of fungi. 



Later on, however, the fungi take advantage of the 

 crack.s due to the mechanical action of the moisture. In the 

 cracks that have been established by the warping and uneven 

 evaporation, the spores of rots find a protected place in which 

 to germinate. 



The position in which a timber should be placed is also 

 complicated by the fact that what is called sap wood, that is 

 to .say, wood composed of the outside and youngest layers of 

 the tree's growth, is more susceptible to the action of timber- 

 rotting fungi than are the layers of what is called the heart 

 wood. The younger the wood, the more likely it is to lot. 

 This materially modifies the way that timber should be placed, 

 in all cases where such susceptible parts are present. For 

 instance, in the case of a square piece of timber, of which two 

 sides are tangential and two sides are radial, the outer tan- 

 gential side is more likely to be sajiwood, and hence more 

 susceptible than the inner. Thus, in a case where a timber 

 is so placed in a structure that one of its sides cannot be 

 painted, the unpainted side v.-ill probably be subject to fungus 

 attack; for instance, in the case of the lower rail of a fence 

 there is a choice in the way it should be placed. 



It is easy to see that these nn'chanical features of the 

 weathering of timber have much to do with the facility with 

 which timber rots obtain an entrance, and secure protection 

 while doing their destructive work. In this connexion, the 

 following e.xperiments are interesting and instructive. 



Blpcks about 1.5 mm. across were prepared, all of 

 the .same shape and size. In one, the grain was longi- 

 tudinal, in a second, the same dimension was tangential, and 

 in the third it was radial. These three blocks were placed 

 simultaneously in absolute alcohol 1 mm. deep. The 

 object was to see at what relative rates the alcohol would 

 penetrate the wood along the.se three lines. Previous to 

 immersion in the alcohol, all the faces of the blocks, except 

 the lower and upper, were covered with wax, so that the fluid 

 should not creep round the ends of the ' grain ' in the case of 

 the two latter specimens. ^With the grain, the alcohol tra- 

 ver-sed the block in four and a half seconds. Tangentially, 

 the alcohol penetrated 2 mm. in three hours. Itadially, 

 the alcohol had made little, if any, progress in three hours. 



Water in pieces of the same length moved longitudinally 

 much more slowly. It traversed the length of the jiiece, with 

 the grain, in from five to ten minutes. Adjacent layers of 

 summer wood showed marked ditferences in the rate of 

 progress. Radial and tangential directions not tried. 



Two square pieces of wood, 1 mm. thick, were prepared 

 with the aid of sharp planes, one piece tangential, the other 

 radial. One of these pieces therefore presented the edc^e of 

 the grain, the other its face. The object of the experiment 

 was to test the relative rapidity of water percolation through 

 these two pieces. 



To this end, all four of the edges of each piece were 

 sealed with hot paraffin. Ordinary watch glasses were now 

 sealed to these pieces of wood with the aid of hot wax. 

 Under each watch glass was a small piece of sponge satui'ated 

 with water. To counteract the warping of the wood, the 

 watch glass and the wood were bound about with thread. 

 The watch glasses were accurately paired, and the paraffin 

 was prevented from entering beyond the required limits by 

 previously ringing the pieces of wood with hot paraffin on 

 a turntable. 



The diameter of the circle of wood exposed to the action 

 of the water inside the watch glass was 36 mm. or an area of 

 about 113-2 sq. mm., being the same in each case. 



The percolation took jDlace at a temperature of 50° to 

 55° F. in a rather dry air. The results after eighteen hours 

 were as follows : — 



Percolation through wood in radial direction, 0-335 

 grams. 



Percolation through wood in tangential direction, 100-5 

 grams. 



From this it will be seen that the amount which passed 

 through the wood in the tangential direction (through the 

 wood when the edge of the grain was presented) 

 was about three times as great as through the wood in 

 a radial direction, that is through the wood when the face of 

 the grain was presented. These relative rates of percolation 

 were maintained for several days. It will be noted that these 

 results are in accord with the rate of penetration of alcohol. 



The facts brought out by the.se experiments are highly 

 suggestive, and have an intimate relation to the sawinc and 

 use of timber in general. 



DEPARTMENT NEWS. 



Mr. H. A. Ealloii, M.Sc, Entomologist on the staff 

 of the Imperial Department of Agriculture, returned 

 from St. Lucia to Barbados by the R.M.S. ' Berbice' 

 on November 2. 



