Abstract:When peanut plants (Arachis hypogaea L.) were treated with aqueous solution of Bo (2000 ppm) by spraying application, the cells of the assimilating tissue were enlarged and the thickness of the leaves were increased. B9 promoted the development of the chloroplast, so that the number of chloroplast, grana and the lamella were increased. As a result, the volume of the “container” of chlorophyll was enlarged. In addition, the chlorophyll content of file leaves also increased after B9 treatment, there fore the leaves turned dark green.