杂草由一个国家传入另一个国家,这在世界农业史上的实例是很多的。通常,在这些情况下,杂草遇到更适宜的条件,迅速繁殖和蔓延。又由于在新的条件下没有专门昆虫和病原体等抑制因素,往往加重其危害性。可以举一个典型例子来证实这一点,十九世纪末,澳大利亚为了建造篱墙从美洲运进仙人掌。在这里,它像恶性杂草一样地蔓 Weeds spread from one country to another are examples of the world history of agriculture. Often, under these conditions weeds encounter more favorable conditions for rapid propagation and spread. And because under the new conditions there are no specific inhibitors such as insects and pathogens, tend to increase its harmfulness. As a typical example to prove this, in the late nineteenth century, Australia imported cactus from the Americas in order to build a fence. Here, it’s like a vicious weed