The sunflower has a reputation similar to that of the Australian gum-tree. "The Observatory at Washington, U.S., was placed in a very unhealthy marshy situation, and at certain periods of the year fever was rife in the neighbourhood, but after the ground was annually sown with sunflower the sanitary condition was much improved." It is also stated by the same authority as that of the above fact, that "a Dutch landed proprietor upon the banks of the Scheldt, planted some plots of sunflowers near his houses, and that the tenants enjoyed afterwards complete immunity from miasmatic fever, although that disease continued to be prevalent in the neighbourhood. In the swampy regions of the Punjab district in India the sunflower is grown in some places in large plantations with marked success, its influence tending to remove malaria, and thus benefit the health of residents in those districts. The Agri-Horticultural Society of the Punjab, after investigating the subject, published a report in which the extension of the cultivation of this useful plant was strongly recommended.
This curious subject would hardly have fallen in its place in any of the subsequent chapters and is therefore alluded to here, in connection with another one to be presently mentioned, rather than be omitted altogether. The influence of vegetation on climate has already received attention in another place, and needs no repetition, although it has an affinity with the facts just referred to. At the same time we might have shown how, and why, such kind of vegetation, as that of the mangrove, aids in perpetrating such a malarious atmosphere as the Eucalyptus is believed to cure. As an illustration of the manner, and the extent, to which the vegetation of a country may be modified and completely changed by external circumstances, we may refer to South Africa, of which Dr. John Shaw has given a graphic account, the modifying influence being in this case the introduction of the Merino sheep. After alluding to the introduction of a noxious bur-weed (Xanthium spinosum), he says that when these sheep were first introduced they fed mainly on grasses, but in a country with periodical rains and a high sun these plants had to give way and succumb. Shrubby plants were not eaten as long as the grass was prominent. But the grass vanished rapidly, and the scrub came to be the main resource of the flocks, and the ground was given over to bush, and scrub, and obnoxious herbs. The climate then became affected, the hardy plants of the southern desert tracts spread northward, and the pleasant country was rapidly becoming an extension of dreary, scrubby, half-deserted Karoo. "Some tracts of the country," he says, "are poisoned by the extraordinary increase of the Tripteris flexuosa, and transport riders, with their oxen, our only carrying power, have to travel through certain parts without pausing, on account of the Melice, grasses which have increased to an extent scarcely to be fancied in the last few years, and on eating which cattle become affected with intoxication to an alarming extent." This is only one example, out of many which might have been adduced, to show how the surface of the earth is undergoing great modification and alteration, through the disturbing influences of civilisation and colonisation, some of these, such as the destruction of forests, having produced disastrous consequences on the climate.
During 1877, a paragraph went the round of the papers respecting a singular tree, which, although it did not profess to destroy miasma, was no less beneficial, inasmuch as it provided moisture in dry places, and the "Rain-tree," it was anticipated, would convert all deserts into paradise. As there is "nothing new under the sun" the same story, or nearly so, has been found on record more than a century previously, to the following effect: "Near the mountains of Vera Paz (Guatemala) we came out on a large plain, where were numbers of fine deer, and in the middle stood a tree of unusual size, spreading its branches over a vast compass of ground. We had perceived, at some distance off, the ground about it to be wet, at which we began to be somewhat surprised, as well knowing there had been no rain fallen for near six months past. At last, to our great amazement, we saw water dropping, or, as it were, distilling fast from the end of every leaf." The new story, on the authority of the United States Consul, related to Moyobamba in Northern Peru, where "the tree is stated to absorb and condense the humidity of the atmosphere with astonishing energy, and it is said that the water may frequently be seen to ooze from the trunk, and fall in rain from its branches, in such quantity that the ground beneath is converted into a perfect swamp. The tree is said to possess this property in the highest degree during the summer season principally, when the rivers are low, and water is scarce, whence it was suggested that the tree should be planted in the arid regions of Peru, for the benefit of the farmers there."
Thus much for the story, as it obtained currency, which requires some modification in face of the facts. The whole subject was investigated, and narrated by Mr. W. T. Thiselton Dyer, in the year 1878. From this we glean the following facts:—The scientific name of the "Rain-tree" was determined as Pithecolobium saman. The Director of the Botanic Gardens at Caracas states: "In the month of April the young leaves are still delicate and transparent. During the whole day a fine spray of rain is to be noticed under the tree, even in the driest air, so that the strongly tinted iron-clay soil is distinctly moist. The phenomenon diminishes with the development of the leaves, and ceases when they are fully grown." He attributes the rain to secretion from glands on the footstalk of the leaf, on which drops of liquid are found, which are rapidly renewed on being removed with blotting-paper.
Another explanation, furnished by Dr. Spruce, the South American traveller, appears to set the question at rest. "The Tamia-caspi, or Rain-tree of the Eastern Peruvian Andes is not a myth, but a fact, although not exactly in the way popular rumour has lately presented it. I first witnessed the phenomenon in September, 1855, when residing at Tarapoto, a town, or large village, a few days eastward of Moyobamba. A little after seven o'clock we came under a lowish spreading tree, from which, with a perfectly clear sky overhead, a smart rain was falling. A glance upwards showed a multitude of cicadas, sucking the juices of the tender young branches and leaves, and squirting forth slender streams of limpid fluid. My two Peruvians were already familiar with the phenomenon, and they knew very well that almost any tree, when in a state to afford food to the nearly omnivorous cicada, might become a Tamia-caspi, or Rain-tree. This particular tree was evidently, from its foliage, an Acacia. Among the trees on which I have seen cicada feed, is one closely allied to the Acacias, the beautiful Pithecolobium saman. Another leguminous tree visited by cicadas is Andira inermis, and there are many more of the same, and other families, which I cannot specify. Although I never heard the name, Tamia-caspi, applied to any particular kind of tree during a residence of two years in the region where it is now said to be a specialty, it is quite possible that, in the space of twenty-one years that have elapsed since I left Eastern Peru, that name may have been given to some tree, with a greater drip than ordinary; but I expect the cicada will still be found responsible for the moisture pouring from the leaves and branches in an abundant shower, the same as it was in my time."
Although, unfortunately, this explanation takes the romance out of the Rain-tree, it must be admitted that Dr. Ernst is of opinion that the rainy mist in Venezuela is produced without the intervention of insects, and that there is still some mystery to be explained. Under any circumstances, the story is of sufficient interest to warrant an allusion to it in the introduction to the subjects of the present volume, which may contain other phenomena not readily accounted for. Cicadas were great favourites with the ancient Greeks, by whom they were believed to be harmless, and to live upon dew; they were addressed by endearing epithets, and regarded as almost divine.
Happy creature! what below Can more happy live than thou? Seated on thy leafy throne, Summer weaves thy verdant crown; Sipping o'er the pearly lawn The fragrant nectar of the dawn.
Plants, regarded in their relationship to different nations and races, have been the theme of more than one writer on botanical geography. There are many suggestions in such a view which are of interest, and we may, in passing, allude to two or three instances. The South Sea Islands are associated with the breadfruit tree, which is the staple food-plant to the natives of Oceania. The lower Coral Islands have the cocoanut palm, which grows abundantly in the Indian Islands between Asia and Australia, and on the coasts of India. The New Zealand flax (Phormium tenax) is characteristic of the islands from which it derives its name. Amongst the Island Malays we find the clove and nutmeg. Maize was the original possession of the American races. Before the time of the Europeans the maguey plant was the vine of the Mexicans, and in recent times another species of the same genus (Agave Americana) has acquired the name of Mexican aloe, and furnishes a well-known fibrous material. Above the limit of rye and barley, in Chili and Peru, grows another characteristic plant—the quinoa—the seeds of which are used as food. On the lower Orinoco the savage races subsist on the Mauritia palm. In Africa the date-palm is the inheritance of the Arab. In Abyssinia the coffee appears as the characteristic plant. With the Hindoo it is rice or cotton. In China the tea-shrub is the supreme national plant. Amongst the Indo-Caucasian races of Western Asia and Europe the original characteristic plants are wheat, barley, rye, and oats. Southern Europe has the olive, and, together with Central Europe, the vine. The Laplanders have no characteristic plant, if we except the reindeer moss. Yet all this is being changed with increasing civilisation; as the European races obtained the almond, peach, and apricot from Asia Minor, the orange from China, rice from India, and the maize and potato from America, so the colonies of the same races, established in all climates and scattered over the world, carried with them their characteristic plants, or collected around them those of all other races. In this manner maize, cotton, the vine, coffee, the orange, and even tea, travelling from their original centres, threaten every climate for which they are suitable, and characteristic plants become a legend of the past.
It is scarcely half a century ago since the tea-plant was first introduced for cultivation on the slopes of the Himalayas in India, and now it has become a most important industry; and tea-gardens, formerly unknown, are a distinctive feature in the landscape. More recently, and with similar success, the fever bark, or cinchona plant, has been brought from South America and naturalised on the Neilgherry Hills in Southern India, whence it is spreading to other parts of the Peninsula. To a more limited extent the hop has been introduced from England into the north-west of India, where barley was already grown, and now breweries of "bitter beer" are established for the benefit of Europeans in the most remote regions of our Indian Empire. Not only are useful plants thus widely distributed, but with them others, such as we term "weeds" are associated. The small seeds of these plants, unintentionally mixed with the seeds of food-plants, accompany them to their new destination; thus the red Indian of North America is said to have recognised the plantain, travelling westward with the white man's corn, and gave it the name of the "white man's foot." Every century will make it more difficult of determination what are the really indigenous plants in countries where European races have established themselves.