Effects of short-duration exposures to 2MHz ultrasound on growth and mitotic index of Pisum sativum roots

Roots of Pisum sativum were exposed to 2 MHz ultrasound for durations from 0.006 to 60 sec. Growth was noticably reduced by exposure durations of 0.03 sec and longer (at a spatial peak intensity of 20 w/cm²) and mitotic index was noticably depressed by exposure durations of 0.06 sec and longer (at 30 W/cm²). Additional increments of ultrasound exposure were progressively less effective in further reducing growth and mitotic index. Thus, a major part of the damage from a one-minute ultrasound exposure appears to be produced within the first few seconds after the beam is turned on.