主播大秀

Pine leaves are very different from the broad leaves of oak and maple. Instead of being broad and flat and easily damaged by frost, they are needle-shaped and very tough. Instead of having pores all over their flat surface they only have pores in one groove that runs down the length of the needle. The groove is partly filled by a tough waxy deposit and under that are the pores which are very few in number compared to those scattered all over an oak leaf. Even at the height of summer, needles can not make food as fast as broad leaves. But then conifers do not discard their leaves every year but keep them for much longer, thereby saving a lot of energy. Growing slowly but surely instead of swiftly, conifers have produced some of the oldest plants in the world as well as the biggest. Giant sequoias, for instance, can live 3,000 years - so not as long as the bristlecone pine - but grow up to 300 feet tall and can weigh over 1,000 tons. Indeed, in a single year they can put on as much wood as would be found in a 60 foot tree of normal proportions. The giant sequoia is therefore the most massive organism on Earth and it has achieved this record with the simplest of ingredients - sunlight, carbon dioxide, water and a few minerals from the earth.