The compound α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) inhibited mitosis in onion (Allium cepa L. ‘Yellow Globe’) and wheat (Triticum aestivum L. Thorn’) root tips. Photomicrographs showed that trifluralin affected mitosis in the same manner as colchicine. Arrested metaphases, c-pairs, micronuclei, amoeboid nuclei, and polyploidy were observed at various times after treatment. An increase in the percentage of arrested metaphases and a decrease in anaphase and telophase figures after 3 hr showed that mitosis was being blocked at metaphase. Prophase did not appear to be affected. Centrifugation of treated root tips displaced the chromosomes of arrested metaphases indicating that the spindle apparatus was disrupted.

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The intra‐cellalar localization of the herbicide N,N‐dimethyl–2,2‐diphenylacetamide (diphenamid) was examined in 10 mm root tips of corn seedlings (Zea mays L. cv. Shawnee). Experiments are described which culminate in the observation that a significant, measurable effect on root growth occurs within 12 hours after treatment with diphenamid. Corn seedlings were then treated with 14‐C‐diphenamid for 12 hours and the 10 mm root tips excised and homogenized. By use of differential centrifugation and gel filtration, the root homogenate was separated into fractions; as follows; cell wall, mitochondria, microsomal, protein and eluate. The highest concentration of the herbicide was found in the root tips. Furthermore, most of the radioactivity was found in the eluate. Results are discussed as to localization of diphenamid in the microsomal and protein fraction and possible mode of action.

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