Geranium callus produced from explants of stem tip, internode pith with vascular tissue on synthetic media with or without coconut milk and 2,4‐dichlorophenoxyacetic acid grew well for many generations, but only tracheids were induced in them. If callus produced on these media was subcultured immediately on Murashige and Skoog medium with 0.1 mg/liter/α‐naphthalene acetic acid (NAA) and 10.0 mg/liter kinetin (K) and incubated at 16/8‐hr light/dark cycle, shoots were induced in 8‐10 weeks and roots in another 8‐10 weeks. Callus produced on the MS medium with the same supplements of NAA and K, subcultured on the same medium and incubated in 16/8‐hr light/dark cycle, produced shoots in 6‐8 weeks. However, on callus subcultured more than three times, shoots differentiated with greater difficulty and none differentiated after six subcultures. Some abnormal shoot‐like structures were also produced, the cells of which showed virus‐like inclusion bodies. Requirements of the different varieties for differentiating organs differed. Among 12/12‐, 15/9‐, 16/8‐, and 20/4‐hr light/dark photoperiods that induced differentiation, 15/9‐ and 16/8‐hr were more effective than the others. Continuous illumination did not induce differentiation. Differentiated shoots formed roots more readily on a medium with reversed proportions of auxin and kinetin. On agar roots were devoid of root hairs. Root hairs were formed when the shoots and plantlets were cultured on filter‐paper bridges. Many “mother” stock plants were produced. These are being studied for their growth qualities and for possible viruses and other pathogens.

Summary The shoot apices of three species of Cupressus exhibit four zones; the superficial layer, the sub‐apical initials, pith mother cells, and the flanking zone. The superficial layer can be subdivided into the apical initials which contribute by periclinal divisions to the subapical initials below and by anticlinal ones to the surface layer on the flanks. Thus the apical initials form the ultimate source of all the cells of the shoot apex in these species. The subapical initials are composed of a very limited number of cells, and may even be only one cell deep in some apices. The initials give rise to the flanking zone laterally and pith mother cells proximally. The flanking zone exhibits a stratified pattern and is composed of more or less uniform and densely staining cells. The pith mother cells form a very shallow zone. A pith rib‐meristem is absent and the cells mature abruptly into pith cells. During the less active months the apical initials do not exhibit periclinal divisions and hence appear like a tunica. But there is no period of dormancy in the shoot apex of C. sempervirens, of which a seasonal study was made.

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