The strength of the banana petiole has been measured as the breaking strength corrected by covariance for the weight of the Iamina it bears. Strength is less in triploids (as compared with diploids) and still less in tetraploids, thus agreeing with the field observation that polyploids have weaker leaves than diploids. There are also differences between plants of different specific origins. Subsidiary results concern the weight of the leaf and the leaf index (length/ breadth) in relation to ploidy.