| environ. |
lichen Composite organisms formed by the symbiosis between species of fungi and an algae. They are either crusty patches or bushy growths on tree trunks, stone walls, roofs or garden paths. Because they have no actual roots they get their sustenance from the atmosphere and rainwater. Lichens play an important role in the detection and monitoring of pollution, especially sulphur dioxide, as they are highly sensitive to pollution and different species disappear if pollution reaches specific levels (在真菌和藻类中形成的共生的复合生物。它们或者是像外壳一样成片的附着或者浓密的生长在树干、石墙、屋顶或者公园小径。它们因为没有真正的根，需要从空气和雨水中汲取营养。地衣在保护和监测环境污染方面有很重要的作用，特别是对二氧化硫的侦测；因为它们对污染高度敏感，如果周围的污染物达到一定水平，不同种类的地衣就会消失。) |
