1). Morphological investigations and cytological studies were performed on the two gigas mutants, produced in the offspring of the asynaptic wild senna in 1949. Cytological studies have determined that these gigas mutants are trisomic plants with 27 chromosomes (2n + 1). 2). These gigas mutants were characterized by gigas type, delay of flowering time and high sterility. 3). In the pollen mother cells, 1", + 12" and 13" + 1, were observed in most cases; and 1" + 1" + 10" in fewer cases. 4). At, and after the first anaphase, various irregularities could be observed. Lagging chromosomes and irregular sporads were often noticed, but bridge, regression, and tripolarity were rarely seen. 5). In the cytological examination of two offspring, which were produced from the self-pollination of plant No. 21-8, observations showed that one resembled the parent, while the other resembled the normal plant.