Centrifugal ovule inception

Abstract

Nine samples from Sattler (1973) were found to exhibit a remarkable correlation between the sequence of ovule inception and ovary structure. In every case, the sequence of ovule inception is centrifugal from its supposed final position of the floral apex. Thus, it is hypothesized that ovules are initiated centrifugally from their floral apex and that this is regulated in some mechanical way. To prove this hypothesis, ontogenetical development of the ovary was reexamined inSilene cucubalus, where the sequence of ovule inception was expected to be not simply basipetal but basipetal on the central column and acropetal on the septal protuberances.The results appear to support the hypothesis. A basipetal sequence is clearly visible on the central column. Although the ovule number is very small on the septal placenta, an acropetal sequence can be recognized, i.e., the distal primordia are obviously initiated later than the proximal ones.Two possible mechanisms for centrifugal ovule inception are suggested: (1) that it is regulated by chemical information diffusing from the floral apex or (2) that it is dependent on gradation of cell age in the placenta. The second mechanism is discussed and supporting evidence is suggested in the epidermal cell arrangement of the septal wall.