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Art. XL.—On the Occurrence of Starch and Glucose in Timber.
[Read before the Wellington Philosophical Society, 13th April, 1904.]
IN the course of work on the histological character of New Zealand timbers, I was struck with the frequency with which starch is found in kahikatea or white-pine (Podocarpus dacrydioides). It seemed that this might have some connection with the peculiar liability of white-pine to be attacked by the boring larva of a beetle, and I was led to examine as many specimens as possible of worm-eaten timber of this kind. The result was that in nearly every case in which the timber was so attacked starch was found to be present either in the medullary rays or in the xylem parenchyma, and the few samples of worm-eaten white-pine that did not contain starch contained abundant glucose.
In a paper read before the Australasian Association for the Advancement of Science, in January of this year, I suggested that kahikatea might always be relied on to yield the satisfactory results that it has sometimes been found to yield, if it were cut when the stored starch has been converted into soluble glucose for the use of the plant, and if the converted timber were allowed to remain for some time exposed to the action of water to dissolve out the glucose. With the kind assistance of Mr. Holmes, of the Public Works Department, and of others, I am endeavouring to determine at what time starch ordinarily disappears from the tissues.
Since January I have examined many other samples of worm-eaten timber, and find that timber attacked by larvæ of beetles contains either starch or glucose, usually the former. Of course my observations are not at present by any means exhaustive, and there is in all cases great difficulty in ascertaining with any certainty even the approximate time at which the timber was felled. Excluding kahikatea, the samples noted here have been examined.
Rimu (Dacrydium cupressinum): Worm-eaten samples usually contain starch both in rays and in xylem parenchyma. When starch is absent much glucose is present. Five samples.
Matai (Podocarpus spicata): As, in the case of rimu. Four samples.
Totara (Podocarpus totara): Two samples. No starch, abundant glucose.
Kauri (Agathis australis): Seldom attacked. The two samples are both from buildings in which there is much worm-eaten kahikatea. One contains starch in the medullary rays; the other contains much glucose.
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An Australian timber, said to be swamp-gum, was used in the construction of a barge for the sugar-refinery at Auckland. Captain Broun sent to the Agriculture Department a portion of the timber from this barge riddled by the larvæ of a beetle. Starch is abundant in both rays and parenchyma.
American axe-handles, ash, in the museum of the Agriculture Department, part of a shipment attacked by larvæ of beetles, contain starch in rays and xylem parenchyma.
Chip pill-boxes in the same museum, part of a worm-eaten shipment, show much starch in the tissues. They are of coniferous wood.
Maire frequently contains starch. I have not seen worm-eaten specimens, but am informed that this timber is frequently attacked. The same remarks apply to tawa.
These instances, though insufficient to prove that it is usually for starch, and when not for starch for glucose, that the larvæ of beetles attack timber, are, it seems to me, sufficient to justify greater care in the selection of timber. No timber should be accepted for use in a sheltered position if starch is found in it, or if, in the absence of starch, it contains much glucose; and examination for the detection of these substances should not be confined to the surface of the timber or to the outer parts of the tree.