Parenchyma cells of maple wood may live for more than a century though a considerable proportion die earlier. A few cells succumb each year making "heartwood" formation gradual. Post mortem deposits, primarily in the parenchyma cells, account for the deepened color of older maple wood. The pH, water content, and mineral content of the wood do not change appreciably with aging. Maple wood often becomes deeply stained. The stain is due to deposits in the parenchyma cells which, if killed before senescence sets in, produce a post mortem deposit which is darker and larger than that produced by cells dying of old age. Stained wood is distinctly alkaline and contains substantial amounts of minerals which accumulate in the stained region. These regions also have a higher moisture content than normal wood. The consistency with which stain is produced in advance of spreading decay fungi suggests that staining and the related chemical changes exert a considerable influence on decay in sugar maple.

T h e internal air of n-iaple trunks was found to vary consirlerably it1 composition, g)articularly in decaying trees. Ira all cases carbora dioxide occrlrrc~cl in much larger, and oxygen ira .;mailer aniounts than in the akn~osphere. C a r b o~~ dioxicle content was highest in the surnrner and lowest in rnidwintes, oxygen varying reciprocally. Diurnal variations were also noted. Chowth of naaple rot fungi on malt agar was favored by carbon dioxide in conce~ntrakiorls found in living trees.In several rases, optimum concentrations were of the order of 107&, growth being approxiillately double that in carbon dioxicle-free air. Oxygen laad little cf'fect within the range of concentrations occurring in trees. I t is concluded that aeration is probably not an important factor in the developnlent of decay, i)oor aeration tending to be stimulating rather than inhibiting..;1.fn'iluscript

Some of the progressive changes in decay in maple trees were studied by comparing total activity of the decay community (as measured by carbon dioxide output of excised samples), water content, pH, and predominant microorganisms (as shown by isolation on malt agar) in zones selected across the pocket of decay.Four trees from which Fomes igniarius were isolated gave consistent results with alkaline pH, high moisture content, and a predominance of imperfect fungi in the zones of incipient decay. Surprisingly, these zones showed the highest rates of carbon dioxide output, though they were only slightly higher than those of the transition zones. The center, severely decayed, parts of the trees were slightly acid, appreciably drier, and contained F. igniarius in abundance. They showed only about half the rate of carbon dioxide production of the outer zones. A section of rot caused by Polyporus glomeratus corresponded in most respects to those with F. igniarius.In samples of two regions from which no basidiomycete decay fungus was isolated, the pattern was completely different. In these the pH was consistently alkaline all across the pocket, exceeding pH 9 in one central area, and was highest in the central zone. The moisture content of these two trees was very high, being highest in the central zones, and the carbon dioxide production was much higher than that of the F. igniarius decays.

No abstract

Poplar trees with decay typical of that caused by Fomes igniarius, or with extensive stain, were dissected and several hundred platings made from each. Sixty-three different fungi were isolated, as many as 20 from a single tree. Most of the fungi were widely distributed in the tree with no consistent association with any stage of decay. Different zones of decay yielded 19 to 36 fungi each, the zone of early incipient decay giving the largest number. Bacteria were isolated from every zone.Trees with stain but no decay yielded 24 fungi, 15 of which were also found in the decayed trees. Many of these were clearly precursors of F. igniarius. Several pockets of typical decay did not yield F. igniarius, suggesting that it had been killed out by competition.The pH of water extracts of wood from various zones of decay was highly variable, the minimum range for a zone being pH 4.8 to pH 8.8, and the maximum range pH 3.8 to pH 9.4. The implications of these variations are discussed.Effects of various media, and of frozen storage prior to making isolations, were studied.