阅读下面这首诗，完成后面问题。
                                                                                                        菊
                                                                                                      郑谷
                                                                              王孙莫把比蓬蒿，九日枝枝近鬓毛。
                                                                               露湿秋香满池岸，由来不羡瓦松高。
                                   【注 】 瓦松：一种高大建筑物瓦檐处的植物，能开花吐叶，但“高不及尺”，没有什么用处。