Fig. 89. Rose pogonia. A native bog orchid with purplish-pink flowers.
Fig. 90. Yellow-fringed orchid. A bog and meadow orchid of the eastern United States.
comprises over 6,000 species and many varieties, the overwhelming proportion of which live in the tropics. Perhaps 90 per cent of them are epiphytes, or air plants, which are perched high up on the branches or bark of trees, and take all their food and water from the air. All the native orchids of temperate North America grow in the ground, however, and their food habits are unique. They depend for food upon a microscopic organism found inside the roots of all orchids, and which helps them to take in the food from the soil. So many of these orchids are partial saprophytes, and without the associated organism they could not grow. Almost uniformly the
Fig. 91. Whorled pogonia. A woodland orchid with the leaves and flowers whorled at the apex of the stem. Fig. 92. Arethusa. The most beautiful of our bog orchids, with a fringed lip and pinkish-purple flowers which bloom about Decoration Day. Note the highly irregular flowers in this and [Figs. 89-91.]
Orchidaceæ have only a very few sheathing leaves, entirely without marginal teeth, and some kinds are practically leafless. The flowers, among the most gorgeous in the world, are always irregular in the sense that there is no obvious series of sepals and petals. Both these are so much transformed as to be nearly unrecognizable as such, but in some orchids there appear to be three sepals. More often of the three inner segments of the flower two are somewhat alike, while the third is quite unlike them and is known as the lip; it is among the most variable of any parts of the orchid flower. As adapted to insect visitors, the flowers of orchids are the most wonderfully developed of all plants. Because of their beauty and strange shapes, orchids have been much sought after by collectors, and explorations of tropical, fever-ridden forests have not infrequently ended in death to orchid hunters. New and rare species of them are constantly being gathered by these collectors. One expedition to New Guinea found over 1,000 kinds never before known, and in the last few decades over 4,000 new orchids have been discovered. For these plants orchid fanciers pay large sums, and a single plant of a rare one sold in London at auction for over $500. The chances of collecting such species made expeditions to the tropics frequent during the latter half of the last century.