ALBERT

Description: The substance of this paper opened the symposium on ‘Structure and functioning of apical meristems’ at the X International Botanical Congress, Edinburgh, 1964. It is a review, but includes original work on Macrozamia communis. The works of Hanstein (the so-called ‘Histogen Theory’ of 1868), Duliot (1890) and Schmidt (the ‘Tunica-Corpus Theory’ of 1924) are compared and shown to be descriptively similar. Their term ‘initia’ l, in regard to any one layer or to the central region of the apex or to the whole apex (gymnosperms), corresponds to the ‘apical cel’ l in regard to the whole apex of pteridophytes. The continuing meristematic residue (i.e., the apical cell or cells) is proposed for a line (or lines) of cells inheriting the office of initial. Derived from this, the general meristem is the site of elaboration of primary tissues. In both components of the apical meristem no cell is permanent. Three basic types of continuing meristematic residue (i.e., monoplex, simplex and duplex apices) may have phylogenetic-taxonomic significance. Seed plants are interpreted as having ‘apical cells’, not pyramidal, not necessarily single, and not always superficial. Histological differences between ‘reproductive’ and ‘vegetative’ shoot apices are paralleled by differences between vegetative apices during different growth performances, and may be merely growth differences preceding or accompanying reproduction. Macrozamia communis supplies an original example. Root apices may be grouped in at least five types according to tissue derivation, with no major taxonomic significance, and distributable among the three basic types of continuing meristematic residue. A ‘quiescent centre’ (not completely inactive) is regarded as inevitable and not diminishing the significance of initial (apical) cells. The significance of primary augmentive meristem is discussed, and the primary thickening meristem is exemplified by original observations on Macrozamia communis. The following principles are applied to several features in the literature: (1) distinction between continuing meristematic residue and general meristem; (2) pattern being in fixed relation to the advancing apical surface; (3) no cell being a permanent cell in the meristem. The paper concludes with an attempt to indicate the paths for apical meristem research beyond 1964