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The effects of mixtures of glycosides from Nerium oleander L. on root tips of Allium cepa L. and endosperm of Haemanthus katherinae Bak. were studied. The root tips were exposed to the solutions for different time intervals (6 to 48 hours) and their recovery in tap water was also observed. Disturbances in Allium were studied exclusively by means of the squash preparation technique. Endosperm of Haemanthus was studied both in vitro and in the electron microscope. The following disturbances were found: (1) Disturbances in the formation of a normal bi‐polar mitotic spindle. Distinct continuous fibers are not present although kinetochore‐fibers are well developed. It is suggested that continuous microtubules arranged as distinct bundles are necessary for a normal bipolar anaphase. Irregularities at anaphase resulted in: a) Formation of restitution nuclei from whole chromosomes (kinetochore regions unsplit) or chromatids. b) Separation of chromosomes or chromatids into a few irregular groups which form restitution nuclei of different sizes. (2) Disturbances in phragmoplast development, often leading to the formation of multipolar phragmoplasts and a branched cell plate. During recovery in tap water, aberrant mitoses are gradually replaced by normal ones both in polyploid and hypoploid nuclei (even those containing only two chromosomes).

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