生物学家把一些健康的白杨树放置在周围都是遭虫害的白杨树中,三天之内,这些健康的白杨树开始落叶;两种树木都分泌相同的化学物质。分泌开始后,进一步促使健康树木落叶。经过化验,树木分泌的化学物,可以 Biologists placed some healthy poplars in the poplar trees around them and within three days these healthy poplar trees began to deciduous; both trees secrete the same chemicals. After the secretion began to further promote the healthy trees deciduous. After testing, the chemicals secreted by trees can be