Professor Wellington Gray tells us (p. 10) that 3000 square inches of cabbage leaves will give off a pint of water daily.' Professor Pfaff says (Ebermeyer, p. 186), From 18th May to 24th October, an oak with 700,000 leaves, each of a square surface of 2325 millimetres, evaporated 120 kilogrammes.' Valliant (ibid.) says, An oak 21 metres high gives off 2000 kilogrammes of watery vapour in a fine day.' Dartig (ibid.) says, A German morgen (=2.3895 acres) carrying 1000 trees of nine different kinds of conifers and broad-leaved trees of 20 years' planting, exhales daily during the period of vegetation at least 3000 lbs. weight of water.' Professor Prestwich (Water-bearing Strata, p. 118) says, The leaves of a tree of average size give off 2i gallons of watery vapour daily.' Mr. Lawes says, 3 plants of wheat or barley gave off gallon = 250 grains of water for every grain of solid residue in the adult plant.' M. Fautrat (Observations Meteorologiques, 1877-78, pp. 14-16) has come to the following conclusions 1. That when it rains more rain falls over a wooded than over a non-wooded area, and that whilst trees of all kinds pos.sess the power of condensing vapour, broad-leaved trees produce less effect than is produced by the narrow-leaved coniferm. 2. That, as regards the hygrometric condition of the air, the air over a wooded area contains more watery vapour (p. 18) than an unwooded area, but'that the coniferm have more watery vapour in their circumambient atmosphere than the broad-leaved trees. If the vapour dissolved in the air was visible as are mists, we should see the forests surrounded with a. vast screen of moisture ; and around the coniferm this envelope would be more marked than over the broad-leaved trees. What is the source of this vapour ? Does it come from the soil ; is it the result of evaporation from the leaves, or is it due in the coniferm to the action of the thousands of points which the whorls of their leaves develope every year ? This is a complex question, which the present data of physical science do not enable us to answer. . . . We must therefore ascribe to the soil, and to other unknown causes, this remarkable property which pines have of attracting watery vapour.' Rolleston says the leaves of the coniferae wet readily, and intercept one-half of the rain which falls upon them, whilst the broad-leaved trees intercept but one-third (p. 37).
G. H. Rowell (Cause of Rain, 1839 and 1872, Brief Essay on Meteorological Phenomena, 1875) supposes that the molecules of watery vapour are completely enveloped in a coating of electricity, to which they owe their bnoyancy. And he supposes this coating and buoyancy to increase and decrease in ratio with the temperature of these molecules. On this theory, efficient con duction of electricity -will suffice to precipitate watery vapour either as rain, or as mist, or as dew.
Becquerel's view is that the plague of hail which has so often been observed to follow upon the destruction of the woods of a country, is to be ascribed to the loss of the lightning conductors, which the cut down trees represented wlaile standing, and to the absence consequently of the incessant though insensible agency of the trees.
Professor Grandeau says (Chimie et. Physio logie, p. 340), K. E. von Baer (Reden und Studien, 1864-, 1873, and 1876), and Oscar Peschel (Nene Probleme. 1876), seem to regard as hopeless any attempt to clothe treeless districts with trees.
It seldom happens that the core of trees is exactly in the centre ; they seem in Europe to thicken most rapidly in the direction in which they are most exposed to light and heat.
In Europe the thickening is always on the south side of the tree. In India, so far as it appears, it is in general mostly due west. In all likelihood the excess of solar heat furnishes the explanation in both cases. North of the tropics the sun always shines more or less from the south, and gives out more heat from this thau from any other direction. Froni the tropics to the line, the sun is so nearly vertical, that the mass of heat contributed to a tree or any other body perpendicular to the earth, is from east or west. But from dawn till noon the temperature of the sun is comparatively moderate,—it is from mid day till sunset that the vast mass of heat is thrown off, the rays shooting from the westward. In this direction a tree thickens on the same prin ciple that it expands in Europe to the southward.
The teak tree often becomes in part petri fied,—that is, the deposition of silica becomes so abundant as to turn a portion of the trunk into stone, usually resembling the petrified wood of Egypt, Sind, Gujerat, Burma, and Trevicary, etc. In Upper India this is not at all confined to the bamboo or the teak, both remarkable for their siliceous secretions, forming in the former a beautiful enamel ill over the stein, furnishing the sharp points of the leaves, and making the upper surface of the leaves of the latter eminently serviceable as sand-paper. The Ghunbliar wood found in the Nepal and Chitta gong forests contains such quantities of silica, that the carpenter who contracts to saw it by the foot, makes it a condition in his bargain that it shall contain no stone. The ebony, the tama rind, the sissoo, and the sitsal or jungle rose wood, contain these secretions, though in much smaller quantities. The most mysterious circum stance connected with the specimens from the petrified forests, is that for every atom of carbon or other organic matter that has been removed, an atom of silica has come in its room, the structure remaining so perfect that under the glass it could not bo discovered whether it was a petrified or living specimen under inspection.
The extension of fruit-bearing trees amongst the people is ono deserving special attention. Advantages must arise to the great mass of the population from increasing the capabilities of the country in this respect.
Throughout the central and western parts of Peninsular India, the chief cereals and pulses are grown in the cold season of the year. The culti vators rega.rd hedges and trees as injurious to crops, which are annually enclosed by the branches of thorny trees; consequently, when the crops are off the ground, the whole territory has a treeless aspect, and in many places firewood bears a very high price. There are great tracts, however, which could be beneficially planted with trees.