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rising above that of the surrounding atmosphere.

It would appear, however, from experiments made by Dutrochet, that the heat of plants manifests itself when evaporation is restrained. Evaporation was prevented by placing the plants in an atmosphero saturated with moisture. The experiments were made with a thermo-electric apparatus, and it was found that their temperature rose from ⁠1/12⁠th to ⁠1/3⁠rd per cent. above that of the external air. Moreover, a rise and fall took place in the course of twenty-four hours, the maximum occurring between ten and two in the day, and the minimum at midnight.

Where, however, vegetable combustion is more rapid, the heat of plants is readily detected, even when evaporation is going on from their surface. This is the case in germination, which is always accompanied by a rise in temperature, and also in the act of flowering. The disappearance of the starch and sugar is the result of their combustion, or partial conversion into carbonic acid; oxygen is therefore consumed, and heat necessarily evolved.

The development of heat by flowers was first observed by Lamarck in the Arum maculatum of Europe. It was afterwards detected by Saussuro iu the biguonia, gourd, and tuberose. In these cases the heat was measured by a common thermometer. But since the invention of thermo-electric instruments, heat can be detected in any ordinary cluster of flowers. The best plants for experiment are the Araceæ, where the heat is confined and reverberated by the hood-like inflorescence. In some of these plants the temperature rises at times to 20° and even 50° Fahrenheit above that of the surrounding air. The temperature increases from the first opening of the flowers, and reaches its maximum when they shed their pollen, at which time the heat developed is so great as to be perceived by the hand; it afterwards gradually declines until the flowers fade.

The heat of flowers is strikingly seen in Alpine regions, when they bloom under the snow, by the disappearance of the snow which immediately surrounds them. This is well exemplified in the beautiful blue-eyed Soldanella of the Alps, which forms a complete cavity or hollow around itself when it blossoms under the snow, as was observed by the French naturalist Lortet.

Now although plants do absorb oxygen and give out carbonic acid at night, yet in this in stance the process of combustion is so slight, that although evaporation has ceased, not the slightest heat is produced which is perceptible to the senses, or even to the most delicate tests which science furnishes. The absurdity, therefore, of removing the plants is at once seen. Let them alone! whether in flower or not, they are doing no harm, and will do good if the patient is fond of flowers,—bring back pleasant memories of the bright sun, the clear blue sky, the healthy breeze, of rambles in the field and forest; they are not foes, but friends. I love them. They have often driven away sad thoughts. They will continue to cheer me to the end of life's journey. They will take up their watch by my headstone. No matter if it is only a little groundsel, chickweed, or moss; all are welcome, because all are beautiful! Woven by the magic chemistry of Nature from earth and air, coloured by the distant sun, each is the work of an Infinite Being, associated with the past and linked with the future of an eternal universe; and naturalists will puzzle themselves about the nature of their chemistry, and try in vain to search out the grand secrets of their vitality for ages yet to come, as we do now.

Although the carbonic acid given off by plants at night is too small in quantity to do any harm, yet it is undeniable that unpleasant effects are sometimes produced by the odour of flowers. The powerful perfume of the swamp magnolia of North America (Magnolia glauca) is said to produce in some people sickness and headache, and the odour of the jonquil, lily, and tuberose will produce faintness in others. The writer is acquainted with a gentleman who suffers greatly during the hay season from the perfume of the hay-field, given off principally by the sweet-scented vernal grass, or Anthoxanthum odoratum.

As the exhalation of oxygen from the leaves of plants stops at night, whilst animals still continue to breathe out carbonic acid, it is obvious that if darkness continued the air would ultimately be totally deprived of its oxygen and filled with carbonic acid, which the plants would be unable to remove. The plants would therefore cease to grow, and the animals would die. The morning sun, therefore, brings not only light but life to the world, because it corrects the night breathing of plants; so that, as soon as the sunlight strikes their foliage, they commence exhaling oxygen, the gas which supports flame and human life at the same time. It is this renewed exhalation of oxygen by plants which gives to the morning air its freshness and purity. Therefore, this grand change from night to day alone preserves the earth habitable.

Again, the light of the sun is absolutely necessary to the formation of chlorophyl, or