Ceylon; an Account of the Island Physical, Historical, and / Topographical with Notices of Its Natural History, Antiquities and / Productions, Volume 1

by Sir James Emerson Tennent

Still, all other defects are compensated by the coolness which pervades them; and, under the exhaustion of a blazing sun, no more exquisite physical enjoyment can be imagined than the chill and fragrant flesh of the pine-apple, or the abundant juice of the mango, which, when freshly pulled, feels as cool as iced water. But the fruit must be eaten instantly; even an interval of a few minutes after it has been gathered is sufficient to destroy the charm; for, once severed from the stem, it rapidly acquires the temperature of the surrounding air.

Sufficient admiration has hardly been bestowed upon the marvellous power displayed by the vegetable world in adjusting its own temperature, notwithstanding atmospheric fluctuations,—a faculty in the manifestation of which it appears to present a counterpart to that exhibited by animal oeconomy in regulating its heat. So uniform is the exercise of the latter faculty in man and the higher animals, that there is barely a difference of three degrees between the warmth of the body in the utmost endurable vicissitudes of heat and cold; and in vegetables an equivalent arrangement enables them in winter to keep their temperature somewhat above that of the surrounding air, and in summer to reduce it far below it. It would almost seem as if plants possessed a power of producing cold analogous to that exhibited by animals in producing heat; and of this beneficent arrangement man enjoys the benefit in the luxurious coolness of the fruit which nature lavishes on the tropics.

The peculiar organisation by which this result is obtained is not free from obscurity, but in all probability the means of adjusting the temperature of plants is simply dependent on evaporation. As regards the power possessed by vegetables of generating heat, although it has been demonstrated to exist, it is in so trifling a degree as to be almost inappreciable, except at the period of germination, when it probably arises from the consumption of oxygen in generating the carbonic acid gas which is then evolved. The faculty of retaining this warmth at night and at other times may, therefore, be referable mainly to the closing of the pores, and the consequent check of evaporation.

On the other hand, the faculty of maintaining a temperature below that of the surrounding air, can only be accounted for by referring it to the mechanical process of imbibing a continuous supply of fresh moisture from the soil, the active transpiration of which imparts coolness to every portion of the tree and its fruit. It requires this combined operation to produce the desired result; and the extent to which evaporation can bring down the temperature of the moisture received by absorption, may be inferred from the fact that Dr. Hooker, when in the valley of the Ganges, found the fresh milky juice of the Mudar (calotropis) to be but 72°, whilst the damp sand in the bed of the river where it grew was from 90° to 104°.

Even in temperate climates this phenomenon is calculated to excite admiration; but it is still more striking to find the like effect rather increased than diminished in the tropics, where one would suppose that the juices, especially of a small and delicate plant, before they could be cooled by evaporation, would be liable to be heated by the blazing sun.

A difficulty would also seem to present itself in the instance of fruit, whose juices, having to undergo a chemical change, their circulation would be conjectured to be slower; and in the instance of those with hard skins, such as the pomegranate, or with a tough leathery coating, like the mango, the evaporation might be imagined to be less than in those of a soft and spongy texture. But all share alike in the general coolness of the plant, so long as circulation supplies fluid for evaporation; and the moment this resource is cut off by the separation of the fruit from the tree, the supply of moisture failing, the process of refrigeration is arrested, and the charm of agreeable freshness gone.

It only remains to notice the aquatic plants, which are found in greater profusion in the northern and eastern provinces than in any other districts of the island, owing to the innumerable tanks and neglected watercourses which cover the whole surface of this once productive province, but which now only harbour the alligator, or satisfy the thirst of the deer and the elephant.

1: See on this subject LINDLEY'S Introduction to Botany, vol. ii. book ii. ch. viii. p. 215.

CARPENTER, Animal Physiology, ch. ix. s. 407. CARPENTER'S Vegetable Physiology, ch. xi. s. 407, Lond. 1848.

The chief ornaments of these neglected sheets of water are the large red and white Lotus[1], whose flowers may be seen from a great distance reposing on their broad green leaves. In China and some parts of India the black seeds of these plants, which are not unlike little acorns in shape, are served at table in place of almonds, which they are said to resemble, but with a superior delicacy of flavour. At some of the tanks where the lotus grows in profusion in Ceylon, I tasted the seeds enclosed in the torus of the flowers, and found them white and delicately-flavoured, not unlike the small kernel of the pine cone of the Apennines. This red lotus of the island appears to be the one that Herodotus describes as abounding in the Nile in his time, but which is now extinct; with a flower resembling a rose, and a fruit in shape like a wasp's nest, and containing seeds of the size of an olive stone, and of an agreeable flavour.[2] But it has clearly no identity with those which he describes as the food of the Lotophagi of Africa, of the size of the mastic[3], sweet as a date, and capable of being made into wine.