mountains, which protrude through the snow. These hardy plants are mostly in a dormant state, the severe temperatures rising only a couple of days a year just enough to enable the Lichen to enliven their body chemistry and to photosynthesise. Some Lichen is black and this enables them to retain what little of the suns heat they can to melt the snow around them. Some grow on rocks that are frequented by birds as their droppings provide a rich source of nutrients. This activity however happens in the warmest part of the summer and as cold winter sets in they return to their dormant sleep.Other algae manages to survive in the snow itself, they live in between the individual flakes just below the surface and during the summer their chlorophyll is disguised with a red pigment to protect the algae from the ultra-violet rays of the sun, as they shine more strongly through the snow. As the sun shines however, it melts the snow and does give them the liquid water they need. In the winter, when the snow is below zero the algae manufacture a kind of anti-freeze which prevents their bodies from freezing and they are invisible below the surface, but when the summer arrives once more they launch themselves forward with microscopic beating hairs and move closer to the surface and the light.At the other end of the earth, The North Pole, the situation is different. After the Ice Age, as the ice retreated, plants began to colonise the land it revealed and as they did they evolved in to different forms, better equipped to grow in their new environment. A species of willow developed that grows not vertically but horizontally, restricted to the ground, less the fierce Arctic wind should level it. It may become as long as a European relative would grow high, but it never raises more than four inches of the ground.In the Arctic summer, the plants that live there have a moderate supply of the four requirements. The temperature is well above freezing,...
