sandy soil, we find the Fir (Pinus silvestris), beautifully red inside; in the same condition we find the Fir (Pinus mughus), on turf soil, where there is an abundance of water; but when we look at it on lias soil it shows broad yearly rings and hardly any colour at all. The Larch tree again in such soil develops itself well with a rich colour. The cause for these appearances must, therefore, rest with the chemical condition of the soil and its effect upon the individuality of the Fir. Oaks generally furnish good timber when grown slowly in dry ground, whilst those from wet soil appear considerably spongy. Similar results are obtained with other trees.

Trees cut in summer give lighter wood than when felled in winter time. The cause for this may probably be ascribed to the fact that in winter a large amount of nourishment is stored in the stem, which, during the spring and summer, is spent for the formation of blooms and leaves.

We call hardness of the wood the resistance which it opposes when another body enters it. If wood were an equal body, like minerals, we should be able to determine its resisting power or hardness; but it being differently built, and whilst trying its hardness other properties interfere, we cannot arrive at a decisive result. Sometimes a wood has very hard fibres but little body, that is, it is lighter built than another wood with soft fibres and a full body. It is, therefore, unadvisable to judge the hardness of a wood according to its fibres. Experiments to ascertain the hardness should be made across the stem, and not upon a longitudinal section, and, although there is no instrument which leads us at once to a definite result, we can generally arrive with a saw at a fair conclusion. Many persons constantly employed on wood are of the opinion that it becomes harder if it is worked or barked off whilst green.

Wood, as a porous body, contains, in its natural state, whether dead or alive, a certain amount of moisture. By the loss of that moisture, or with the increase of the same, the bulk of the wood either contracts or extends. If we have a piece of wood where this action takes place only upon one side it is obvious that the piece will alter its form or shape. The consequence of the loss of moisture is also the warping and the splitting of the wood. The inner structure of a stem is irregular; for instance, we find the inner moisture of a yearly ring to be more than on its

outer side. This causes the splits on the exterior after the wood is dry, and it also accounts for the impossibility to form out of greenwood a regular body which could not lose its weight or shape. The time during which the evaporation of the moisture takes place depends upon the state of the atmosphere

Several authors are of the opinion that the contraction is regulated by the specific weight. This, as a rule, cannot be adopted; for instance, Lilac and Oak, both being heavy and hard, contract quickly, whilst the South American Maple, which is equally hard, contracts slowly. It is evident, however, that the fuller of sap a tree is, the greater will be the contraction. This will account for the fact that we find on cut timber the cracks extend from the exterior towards the centre, because the sapwood will contract more than the heart of the wood. Planks turn with their sides upwards, that is, the edges rise from the level of the centre line. This explains why we turn the inside of a plank towards the joists whilst we lay a floor, which prevents the twisting.

The contraction and action of the wood cannot be checked altogether. Among the means to prevent it, stands foremost the one of putting the tree into water; but when taken out it must not be stored in a place where it dries too soon, as it still would burst if done. Nor must it be left too long in the water as this will injure the quality of the wood.

All the wood which is used is never quite dry; besides this, it works a little in itself, under the changes of the atmosphere, and therefore attention must be paid to the selection of timber for the same purpose, for the heartwood is less subjected to such actions than sap or splintwood. This is an important point with furniture makers. The extension or contraction is less apparent in the length of the fibre than in the cross section of the wood.

I

PWAI-NGYET.

HAVE noticed your remarks on the substance called Pwai-ngyet in your interesting little periodical "Science Gossip." As it was I who furnished the bees which were forwarded by the Agri-Horticultural Society of

Calcutta to Mr. F. Smith of the British Museum, for identification, and which he pronounced to be Trigona læviceps (as Dr. Mason, to whom you refer, states in his book on the natural productions of the Tenasserim provinces); and as, therefore, I know both the substance and the insect well, I have great pleasure in giving you such information as I can on the subject.

A few years ago the secretary of the Calcutta Agri-Horticultural Society wrote to me for information regarding Pwai-ngyet. Until then, I knew very little about it, but my attention having been called in this way to it, I made it my business to find out what it was.

If I read your remarks rightly, you appear to be of opinion that Pwai-ngyet is the pure unaltered gum or resin of Canarium strictum, only bored and channelled by the bee. If this were so, then the substance should only be found on that tree. It is, however, found on different trees; sometimes too in the ground, or in a hollow among rocks; and, occasionally, even in the hollow post of an old house.

I have seen the bees making their nests in all these several situations.

Pwai-ngyet, I believe myself, is a combination of various gums or resins, and probably also of oils, gathered from various sources, while in a soft state, by the bee, and built up and moulded, very much as wax is moulded; with this difference, that whereas wax is formed by the honey-bee into cells of perfect and uniform symmetry, the cells in Pwai-ngyet assume no regular form at all.

What trees contribute their juices to form Pwai-ngyet I cannot say for certain, though I incline to think that Thengan-tsee, or the resin of the Thengan (Hopea odorata), is the chief ingredient, and that the oil of the various Dipterocarps, or wood-oil trees, particularly of Dipterocarpus lavis, the wood-oil tree par excellence, also enters into the composition of the material. My reasons for thinking so are, that the texture, the colour, and the smell of Pwai-ngyet are all such as would apparently result from a combination of the two substances mentioned; and that Hopea odorata and Dipterocarpus lævis are among the principal giants of our forests, and common trees. On the other hand, I do not think (though I will not be sure) that Canarium strictum is found in our provinces, although I believe a species of Canarium, a large timber tree, is found in Pegu.

The Trigona læviceps builds its nest generally in the hollow of a tree, entering by a small aperture. These

apertures are lined with Pwai-ngyet, and sometimes only show a small rim of that substance raised above the bark of the tree. Sometimes however, (perhaps always if undisturbed), the bees go on building outside, and adding on to the rim, until they have found a wide-mouthed entrance which projects as much as a foot from the tree. These structures commonly assume the shape of the mouth of a large trumpet flattened horizontally, and have a perpendicular diameter of a foot or so, and a horizontal diameter of three or four inches. They are built with great regularity in their exterior half, but not so regularly towards the base, from the necessity of adapting the structure to the shape of the tree where the hole may chance to be. They are very curious and pretty objects, but being very prominent, attract the notice of the passer-by, and so, often lead to the spoiling of the habitation.

Nest of Trigoua laviceps, one-sixth antural size.

I send you a rude sketch of one of the trumpet-openings. I despatch also, by post, together with this notice, a small piece of Pwai-ngyet, broken off the upper base of such a work. By holding this up to the light, you will see three

or four large cells of about an inch in diameter, without any opening. I can only suppose that the object of these cellwalls is to strengthen the narrow base in its support of the larger projecting mass. If so, here is another instance of a mysterious intelligence possessed by one of the smallest of living creatures.

This piece, marked No. 1, will show the ordinary texture colour, and general appearance of Pwai-ngyet, as it is found in the jungles. No. 2, is nearly white, a very unusual, colour. I send it because of the greater resemblance to Thengan-tsee, or the resin of the Hopea odorata; of which I also send a small piece (No. 3), in order that you may be able to ascertain how far the two substances are chemically identical.

What the internal economy of the nest of Trigona læviceps is I cannot say, as the tree has commonly to be felled in order to obtain the contents, and this I have never seen done. I am informed by the Burmese that from five to ten viss are usually obtained from one nest. A viss is about 3 lb., and costs about 4 annas (6d.) in the bazaar. I should imagine that, considering the source whence it is procured, the supply must be very limited; and, if exported, it would soon equal beeswax in price.

Its principal, if not only use, at present, is for caulking; and, for this purpose, it is mixed with earth-oil or petroleum.

The method is to boil the Pwai-ngyet in water, which makes it quite soft, and then to knead it with a certain quantity of the petroleum, until it attains the consistency of a lump of putty, which it much resembles. In that state it is fit for use, and is extremely viscid and tenacious. On putting a piece of Pwai-ngyet into boiling water, in order to perform the operation myself, I noticed that the surface of the water was covered with a thin film of oil. This confirms me in the idea that oil is united with resin in the composition of Pwai-ngyet. It is soluble in oils and in turpentine, but not in spirits of wine. I may conclude by mentioning that the mistakes made by several persons in Burmah with regard to the origin of this substance must have arisen from the fact that the name of Pwai-ngyet is often used here, in the bazaars, to denote any kind of resin or Dammer, but the true Pwai-ngyet of the Burmese is that made by the small bee called Trigona læviceps, and is made by them in the manner I have tried to describe.

Moulmein.

C. S. P. PARISH.