GRE Reading Comprehension: JiJing 352-GRE阅读机经352篇 - TNPS7744J5A5424LK

Normally, seeds of Emmenathe penduliflora stay dormant for years and germinate only when a fire burns through their habitat. Nitrogen dioxide in the smoke induces the seeds to germinate. Fires clear the brush, allowing germinating seeds to receive the sunlight they need to grow. The plants mature quickly, produce seeds, and then die. In areas with heavy automobile traffic, however, the seed germinates in the absence of fire, with automobile exhaust supplying the required nitrogen dioxide.