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The primary division of orchids is into two general classes, — those growing upon trees, and those growing upon the ground; in other words, epiphytal and terrestrial. In hot countries, the species are generally epiphytes; in temperate regions, we find only the terrestrial classes. These rules are not, however, without some exceptions: epiphytes often grow upon rocks or in earth (though, in both cases, the position is rather for support than one of nourishment), and terrestrial orchids abound in hot countries.

The peculiar characteristics of orchidaceous plants will be fully described in a future chapter. Suffice it at present to say, that there is no order of plants the structure of whose flowers is so anomalous as regards the relation borne to each other by the parts of reproduction, or so singular in respect to the form of the floral envelopes. Orchidaceous plants inhabit all parts of the world except those which are excessively dry or excessively cold, both of which extremes of temperature appear uncongenial to their nature. They abound chiefly in regions with a mild climate, moist and warm during the greater part of the year.

The flora of the temperate regions abounds in terrestrial orchids, which are, however, with some exceptions, distinguished by flowers more remarkable for peculiarity of form than for size, and brilliancy of color. It is, however, in the tropical forests that we meet with these plants in full luxuriance: here the species are mostly epiphytal. Establishing themselves upon the branches of the trees, they either vegetate amid masses of decaying vegetable matter, or cling by long succulent grasping roots to the naked branches of trees, from which and the moist atmosphere they derive their nourishment.

They are also found abundantly on the banks of streams near falls of water, where they are constantly bathed in the rising spray. Some few species, indeed, seem of a different nature, growing mostly on rocks exposed to a broiling sun, their roots alone absorbing the moisture of the dew.

In general, a certain degree of shade seems to be essential to orchids. In Brazil, they are found abundantly in damp woods and rich valleys, embowered among foliage of the most luxuriant description. In Nepaul, as stated by Dr. Wallich, the epiphytal species grow in company with ferns; and the thicker the forest, the more stately the trees, the richer and blacker the natural soil, the more profuse the orchidaceae and ferns upon them. There they flourish by the sides of dripping springs, in deep, shady recesses, in inconceivable quantity, and with an astonishing degree of luxuriance.

We should, however, err, did we suppose that the principal haunts of orchids are'the deep, shady woods. It is even probable that just the contrary is the fact, and that the cases just cited are extreme.

Orchids are chiefly found on the borders of the forests, or in the open glades or savannas: it is seldom they are met with in the primitive forests. They are very abundant in Brazil near Rio Janeiro, in Mexico, in Colombia, in Trinidad, especially in mountainous places and damp woods; in the East Indies, in Java, Ceylon, Nepaul, and China, where they are principally found in the woods, on the borders of rivers and mountain-streams. The localities of orchids are very marked: of some species, only a single habitat is known; many are exceedingly rare; some only being known to botany by a single dried specimen in an herbarium; and others once known in our hot-houses are now lost to cultivation. Some species now in cultivation have sprung from a single imported plant. The orchids of the Eastern and Western Hemispheres are entirely different, there being no affinity between them. Orchids are also most capricious in their locations: sometimes a river may be ascended for miles, and not an orchid be seen; when, on a sudden turn of the stream, every tree becomes covered with them. The part of the tree on which they live is also uncertain: some are found close to the ground, others a few feet high, others in the forks of the trunk and branches; some only on the trunk, others only on the branches; and many only on the topmost branches of the loftiest trees, so high that they are only discoverable by their delicious perfume.

Some varieties will only thrive when grown on the lower side of a block, their native growth being on the under side of a branch: of these the fine yellow cattleya (C. citrina) is our most familiar example.

Where they find a congenial home, they grow to immense size; increasing by the pseudo-bulbs in every direction, and often covering a whole tree. In many cases, a large tree becomes a large bouquet of orchids; or many species, with various-colored, curiously-shaped flowers, are often found on the same tree.

While all the East-Indian orchids require a hot, moist temperature, many of the South-American and Mexican species will endure much cold without injury: they are sometimes found where the mercury at night descends below the freezing-point, and where the leaves are covered with hoar-frost. Thus the different species demand far different treatment; and from ignorance of these requirements and peculiarities have arisen many of the failures which have hitherto attended their culture.

A high, mean temperature throughout the year, and a climate either constantly humid or at least periodically so, are atmospheric elements eminently favorable to the production of these plants. All those species which simply exist by clinging by their roots to the branches of growing trees, and probably other species, must derive necessarily their nourishment in a great measure, if not entirely, from the moisture in a very elastic state that surrounds them. And although Nature seems, in general, to have provided for the scantiness of their food by the construction of them with a cuticle capable only of parting by slow degrees with the fluid they receive by their roots, yet it is obviously requisite that they should be so situated as to be within reach of an abundant supply, not only at the time when they are growing, but, to a certain extent, at other periods. Thus we find that the hottest countries if dry, and the dampest if cold, are destitute of them; while there is no instance of a country both hot and damp where they are not plentiful. It may, however, be remarked, that the terrestrial orchids will bear a far greater degree of cold and drought than the epiphytal species; their range is therefore much greater: and the general remarks about orchids must be taken with a great degree of allowance in respect to this class.

Notwithstanding the high temperature of Africa, they are unknown in the sandy deserts and parched atmosphere; yet they abound in Sierra Leone, where the climate is damp, and are not unfrequent in the jungles at the Cape of Good Hope.

In the West-India Islands they exist in great quantities, particularly in Jamaica and Trinidad; not, however, so much on the coast as on the lower ranges of hills.

At Rio Janeiro, the mean temperature is 740 3', and much higher inland; the woods are so damp, it is impossible to dry plants ; and, in such situations, multitudes of orchidaceous plants occur. In the immediate vicinity of Buenos Ayres, however, where the mean temperature is 670 6', and the air dry, epiphytes are unknown. No country, however, exhibits in a more striking manner than the East Indies the necessity of a hot and damp climate for the production of epiphytes. In the Malayan Archipelago, the mean temperature of which is estimated at between 77° and 780, where the atmosphere is always very damp, they are found in profusion. In Nepaul, they occur upon the sides of the lower mountains, where they grow amongst clouds and constant showers; while on the continent of India they are almost wholly unknown, except in the mountain-valleys.

In Mexico and Central America, the provinces most prolific in orchids are Oaxaca, Honduras, and Guatimala: they are also plenty upon the Isthmus.

The conditions of orchid-growth can thus be easily stated. In their native countries they are exposed to a dry season, during which they rest; and to a rainy season, when the heat is higher, and the air moist nearly to saturation. To grow orchids in any perfection, their native climate must, to a certain extent, be imitated: that is, they must have a period of rest in a dry and comparatively cool atmosphere; and, during their growth and flowering, they should be exposed to a high, moist temperature. As orchids principally grow on the trunks and branches of trees, it is important that they should be exposed to a free current of air, and also to the light. The plants should not, however, be exposed directly to the sun's rays, which are apt to scorch the leaves arid wither the flowers; and some species require constant shade.

The great heat and moisture are only necessary while the plants are in vigorous growth; and this period should be during spring and summer, the best period of rest being from November till March. It should be understood that it is this long season of rest which predisposes the plant to blossom. Of course, these rules of growth and rest can be stated only in general terms. There are certain kinds which grow uninterruptedly throughout the year; and again, even of those which go to rest periodically on the completion of their growth, it does not always happen that their time of rest corresponds with that of the largest number. As we come in course to mention the different species, their proper time of rest, if peculiar, will be indicated.

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