Dowco 290 (3，6-dichoropic.olinic acid), a new product of the Dow Chemical Company U. S. A., is a herbicide. The treatment of intact soybean hypocotyl with this herbicide leads to a very marked aberration in the growth pattern. After Dowco 290 treatment, cell division in the meristematic zone is inhibited; cell elongation ceases in the meristematic and elongation zones, and radial enlargement of cells occur in the elongation and mature zone. This abnormal proliferation of the mature hypocotyl is associated with the increment of nucleolar size (the diameter was 1.5 to 2.5 mμ for untreated and 4 to 6 for treated nucleoli), however there was no significant alteration in size of the nuclei (about 6x8 to 10 mμ). The relative DNA, RNA and protein values are about 1:3:11 for the untreated nuclei, however, the nuclei isolated from Dowco 290 treated tissues contained almost twice as much RNA and protein as the untreated nuclei. The treatment of Dowco 290 on soyean hypocotyls is also associated with an enhancement of chromatin bound RNA polymerase I activity. The nuclei isolated from Dowco 290 treated tissues showed about five times as much RNA polymerase I activity as the nuclei isolated from untreated tissues. But there was no significant difference in the level of RNA polymerase II activity expressed in the nuclei from untreated and treated tissues. RNA polymerases were solubilized from isolated nuclei and then were fractionated on DEAE-ccllulose column, the results show that treated and untreated tissues contained nearly equivalent levels of RNA polymerase II, but the treated nuclei have a 3 to 4 fold higher level of RNA polymerase I than the untreated nuclei.