41 



and }ireaks into more or less rectangular pieces. When in its final 

 stages, it is exceedingly l)rittle and can be crushed to a tine powder in 

 a mortar. It is always nuich firmer than wood destroyed by Polyporus 

 schveinitzu and differs from the latter in the character of the cracks 

 or breaks, which are most readih^ seen on a tangential view. 



The progressive changes which take place in the wood of a Spruce 

 may be noted as follows: The wood at first turns slightl}^ red-brown 

 in irregular patches, as seen when a trunk is split longitudinally. • 

 These, patches grow larger, spreading from ring to ring and in a longi- 

 tudinal direction along each ring. Small cracks next appear in these 

 areas, extending part way through the thickness of each ring, both 

 from the side of the spring and of the summer wood. These cracks 

 are ver}- much more visi])le on the tangential view of an annual ring 

 (PI. XI, fig. 1). At first but scattered cracks are to be seen extending 

 longitudinally, which, however, soon elongate and pass both diagonally 

 and directly across the direction of the fibers (PI. XI, fig. -I). At this 

 stage the wood is still hard and has acquired a light-brown color. 

 Immediately about the fissures it is more deeply colored than else- 

 where. A microscopic examination shows that there has been great 

 shrinkage in the volume of the cell walls and that the breaks and 

 fissures occvir practically throughout the whole mass of the ])rown 

 wood; though onh' the larger breaks are visible to the unaided eye. 

 The shrinkage goes on rapidly, and after a time the tension becomes 

 so great that the annual rings separate one from the other. A break 

 usually occurs in a radial direction also, and as a result the free ends 

 of the ring sw^ing outward. Breaks along the lines of the larger 

 medidlary rays take place at the same time. This gives rise to long 

 flat slabs of wood, each the width of an annual ring, Avhich hang 

 together loosely at one end and at isolated points on their tangential 

 walls (PI. XIII). Very ])adly decayed wood is so thoroughly traversed 

 by larger and smaller breaks that it readily fails to pieces when struck. 

 It nuist be noted, however, that the nature of the cracks is such that 

 individual pieces of wood are, as it were, mortised into each other 

 end to end, and this no doubt makes the wood as firm as it is. 



MINUTE CHANGES IN THE WOOD. 



The minute changes which the mycelium of Polyporus Hulfm^e\(i< indu- 

 ces in the wood cells are such that the}' can not well be mistaken. It 

 has been mentioned that the annual rings break into bands which curve 

 inward as the ])rocess of drying goes on. A tangential view of several 

 of these bands before they have broken will present an appearance such 

 as is shown on PI. XI, fig. 4. A large munber of fissures have formed 

 both across the wood fibers and parallel with them. The latter are more 

 prominent — the cross fissures never occurring alone, but generally con- 

 necting several longitudinal fissures. It will be noted that the Invaks are 



