The Natural Philosophy of Plant Form: Cellular Autoreproduction as a Component of a Structural Explanation of Plant Form

A map-L-system is described which simulates the developmentof the two-dimensional patterns of cell walls displayed at thesurfaces of shoot apices of Psilotum nudum. The simulation ofthese cellular patterns commences with the division of a triangularcell and continues until a complete set of ten different cells,including new triangular cells, is formed amongst the descendantsof each merophyte. The triangular cells generated by means ofthis division pathway, P1, are, in their three-dimensional aspect,four-sided apical cells. In the plant, they have the potentialityto support the development of a shoot apex. The generation ofnew triangular cells by pathway P1 therefore seems to be a preconditionfor the branching of the shoot. Observed variations upon thecellular pattern developed by pathway P1 have also been analysed.Two of these variant pathways, P2 and P3, suggest the typesof controls which are required to bring about all three (P1–P3)patterns of cells. These controls may involve the participationof the plant cytoskeleton and may also require an influencefrom the apical cell itself. The triangular shoot apical cellsof Psilotum are autoreproductive cells: that is, at each division,one of the daughters is a new triangular cell, the other daughterhas some other shape. This example of triangular cell autoreproductionand self-maintenance and its relation to organogenesis is discussedin light of the views on reproduction and self-maintenance expressedby Agnes Arber (1950) in her book The natural philosophy ofplant form(Cambridge: Cambridge University Press). Copyright2001 Annals of Botany Company Agnes Arber, apical cell, cell division patterns, computer simulation, cytoskeleton, L-systems, Living Systems Theory, meristems, Psilotum, shoot apex, stem cell