毛白杨是我国特有的杨树树种,栽培历史悠久,它具有生长快、材质好、分布广、寿命长、成大材等优点,是我省发展的主要树种。一、毛白杨的变异是选优的基础生物的种和变种,都是由以前别的种演变而来的。变异的根本原因,是生物内在变异的倾向和外界生活条件的影响,内因是变化的根据,外因是变化的条件,内因和外因互相作用使生物不断发生变异,因此,变异是生物界的普遍规律。大量事实证明,生物的变异也能积累和加强,从而形成新的类 Populus tomentosa is a poplar species endemic to our country, and has a long history of cultivation. It has the advantages of rapid growth, good material, wide distribution, long life and large stock. It is the main tree species in our province. First, the variation of Populus tomentosa is the best selection of basic biological species and varieties, are derived from the previous other species evolved. The root cause of variation is the tendency of biological internal variation and the influence of external living conditions. The internal cause is the basis of change. External factors are the conditions of change. Internal and external factors interact to make the organisms continually mutate. Therefore, mutation is a universal law in the biological world . A large number of facts have proved that biological variation can also accumulate and strengthen, thus forming a new class