The amount of the influence of vegetation, as such, upon the air we breathe, has thus been demonstrated. For every six pounds of carbon which plants have accumulated in their structure, they have withdrawn from the atmosphere twenty-two pounds of baleful carbonic acid gas, and replaced it with sixteen pounds - an equal bulk - of life-sustaining oxygen. Consider the quantity extant merely in the trunks of trees. The trunk of a single giant pine contained 356,000 pounds of carbon - a quantity sufficient to propel, on our railroads, 200 tons of merchandise, a distance of 3,560 miles ! In its growth, this tree withdrew from the air 1,305,833 pounds of carbonic acid gas, and replaced it with 949,333 pounds of oxygen gas - a quantity sufficient to maintain the respiration of a single man for 1,100 years.

Add to the quantity of carbon gathered by this one huge California tree all that is contained in the forests and herbage of the world; all that accumulated in the soil as vegetable mould, peat, and in other forms, the product of the vegetation of by-gone ages. And finally, let the estimate embrace all that belongs to the bodies of the whole existing animal kingdom, and we shall have the expression, if it can be made in figures, of the amount of a single (though the largest) element which vegetation has withdrawn from the atmosphere. If we multiply the vast amount of carbon by sixteen, and divide it by six, we obtain the number of pounds of oxygen gas that have, in this process, been supplied to the atmosphere, and this is the only operation in nature which gives to the air free oxygen gas - that indispensable agent of animal life. Animals consume it, and give back carbonic acid, which, while it is injurious to their life, is the principal element of the food of vegetables, is consumed by them, and the oxygen restored for the use of the animals.

Hence the necessity of the vegetable kingdom in purifying the air we breathe, and hence, too, the impure air of cities, where animal overbalances vegetable life.

The Cactus tribe - growing under the burning rays of a vertical sun, on dry sand nearly devoid of vegetable mould, and beneath a sky that for three-quarters of a year yields them not one drop of rain - are tumid, with a watery juice, of inestimable value to the parched traveller. Even the wild ass, cautiously stripping off the dangerous spines with his hoof, knows how to help himself to a delicious draught, when traversing the desolate steppes.

The Tree, or Cow Cabbage, is one of the most remarkable of the cabbage kind, having a hard and woody stalk, averaging five feet in height, and used for walking-sticks. In the Island of Jersey it reaches the height of eight or ten feet and more. This is mainly produced by daily pulling off the lower leaves as fodder for the cows, leaving foliage only at the top; thus a small garden has almost the appearance of a plantation of palms. Planted close, as living fences, they keep out fowls and small animals. Sheds are thatched with the dried stems; they serve as stakes for kidney beans, peas, etc, and as cross-spars for the purpose of upholding the thatch or roof of the smaller class of farm-buildings, cottages, etc, and, when kept dry, are said to last upwards of half a century. At a distance from the coast, and in colder latitudes than Jersey, this cabbage always degenerates. The walking-sticks are almost handsome.

We have learned, says Dr. Gray, what the food of plants is, and whence they obtain it. Their universal food is rain-water, which has absorbed some carbonic acid, nitrogen, and ammonia or its compounds, from the air, or dissolved them from the decomposing remains of former vegetation already existing in the soil, whence it has also dissolved a variable quantity of earthy matter. This liquid is imbibed by the roots, and carried up through the tissues of the stem; the crude sap is carried into the leaves; these and other green parts of plants (the chlorophylle) constitute the apparatus of vegetable digestion. The agent (the motive power which puts this most curious chemical apparatus into action) is solar light. This is the indispensable agent by which lifeless mineral matter (earth and air) is transformed into the organised substance of living plants, and, consequently, of animals. Such is the important part which light performs in vegetable digestion - that initial step in organised existence upon which, as the first link in the chain, all the rest absolutely depends. Hence the Creative fiat,' Let there be light,' was the immediate precursor, as it is the indispensable condition, of organized and animate existence.

Again: It is clear that the oxygen which is given to the air, in ordinary vegetable digestion, comes from the decomposition of carbonic acid. Plants take this latter gas from the air, directly or indirectly; they retain its carbon; they restore to the air pure oxygen. This is the principal material which is given up to the air, and it alone renders it fit for the breathing and life of animals. To verify this, expose some freshly-gathered leaves to the sunshine in an inverted glass vessel, filled with water, so as to collect the bubbles of air which rise, and which are nearly pure oxygen gas. The evolution of this gas goes on while the son shines, but immediately stops when a shadow is east over the leaves, and is resumed when the screen is withdrawn, or when a gleam of reflected sunlight is cast upon the leaves from a mirror; thus, showing how entirely the whole depends on sunshine. In nature's operations (as in the Daguerrean operation), diffused daylight answers the purpose, but, in our rude experiments, we cannot quite imitate the delicacy of her processes.

"In the parish churchyard of Aldworth, in Berkshire," says a correspondent of a London paper, "stands a yew-tree, which is much larger than any I have ever seen or read of elsewhere. This tree is nine yards, or twenty-seven feet, in circumference, four feet from the ground. The denuded branches spread over a very large surface; their shadow, it is affirmed, at one time covered nearly an acre of ground. Its once lofty head is decayed.