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The depletion of starch in the living sapwood of ash was examined as a possible means of rendering converted timber immune from attack by Lyctus (powder-post beetle).

Observations on disks of timber kept under controlled conditions showed that depletion is conditioned by access of oxygen; thus although in the standing tree depletion proceeds from without inwards, it can be induced in any part of the sapwood, and in any direction, by permitting access of oxygen, i.e. there is no polarity in depletion. The optimum temperature range for depletion in ash is from 31 to 36d̀ C.: above 45d̀ C. death of the cells may interrupt depletion.

The presence of β-indoly acetic acid does not influence rate of depletion. Reformation of the starch in the depleted wood in the presence of cane sugar could not be induced. The enzyme concerned in mobilization of the starch appears to be a labile one with an optimum in the neighbourhood of 40d̀ C. and to be produced during the active respiration of the cells, starch depletion ceasing when oxygen is withdrawn.

In transversely cut disks the rate of respiration at 33d̀ C. ceases to be proportional to the volume of tissue after a thickness of about 6 mm. has been attained. At 20d̀ C. disks 10 mm. thick may be evenly depleted. Infestation experiments upon timber undergoing depletion showed that the attack by Lyctus is circumscribed by starch-level and not by total nitrogen or soluble sugars.

Under correct conditions of kilning, 1 in. sapwood plank can be rendered starch-free in about 20 days: with larger sizes depletion is uncertain and probably uneconomic.

The methods of starch and sugar analysis used in the work are appended.