REGENERATION OF SPHAGNUM

S ummary When disc‐shaped horizontal slices of peat cores, three from a bog in mid‐Wales and three from a bog in Hampshire, were kept for several months in a saturated atmosphere in a cool greenhouse numerous new shoots of Sphagnum papillosum (Lindb. S. magellanicum Brid. and S. recurvum P. Beauv. were produced. The new shoots arose on peat discs from at least 30 cm below the surface and water table and from regions in which the Sphagnum appeared to be brown and dead. A timescale, inferred from the cumulative dry mass and the peak in 137 Cs concentration (which was assumed, conservatively, to reflect the 1963 peak influx), indicates that the matrix of the deepest discs from which new shoots arose was from 25 to perhaps 60 years old. Many of the new shoots of Sphagnum arose as innovations from the outer cortex of buried stems. In most cases the first leaves on these had the usual dimorphic leaf cell pattern. Other shoots, which initially produced leaves with monomorphic cells, arose from protonemata, comprising irregularly lobed plates of tissue and sparsely branched filaments with oblique cross‐walls. A few of the protonemata arose from old stems, a feature not reported before, but the vast majority had no attachment to old plants and are thought to have grown from spores. Light and air were necessary if new shoots were to appear. But very few innovations or protonemata were found in the green discs from near the surface of the core. This suggests some kind of hormonal control of innovations akin to apical dominance in vascular plants and a more general allelopathic inhibition of spore germination and protonemal growth by green Sphagnum. Fern gametophytes of at least two taxa ( Dryopteris‐like and Pteridium‐like ) grew on the peat discs with distribution patterns similar to those of new Sphagnum shoots. Seedlings of five taxa of vascular plants – all species growing close to the core‐sites – appeared on the peat discs but much more erratically than Sphagnum and the ferns. Stems of five species of leafy liverwort, presumed to have been derived from subterranean axes rather than from gemmae or spores, were also recorded, but no other bryophytes were seen. The discovery that morphogenesis in Sphagnum is far more fluid than hitherto assumed has far‐reaching physiological, ecological and possibly genetical implications. The development of protonemata under semi‐natural conditions, recorded here for the first time, confounds the results of culture experiments which had indicated that Sphagnum protonemata were unlikely to grow on peat.