ABSTRACT
The orchids, or Orchidaceae, form a very large family of plants. It has the largest number of species — about 25 000 are known — and is represented in all the continents except Antarctica. As the members are found all over the world, growing in widely different climates, considerable diversity is to be expected within the family. The orchid perianth consists of six segments, arranged in two whorls of three — the outer sepals and the inner petals. Pollination is by insects. When one works its way into the flower to find nectar, the viscidium sticks on to its head or body. In this way, a whole pollinium will be transferred to the sticky stigma of another flower. Most orchids do not need this fungus once they have started to grow. However with a few there is life-long dependence.
