Fine structure in cellulose microfibrils: NMR evidence from onion and quince.

It has been controversial for many years whether in the cellulose of higher plants, the microfibrils are aggregates of 'elementary fibrils', which have been suggested to be about 3.5 nm in diameter. Solid-state NMR spectroscopy was used to examine two celluloses whose fibril diameters had been established by electron microscopy: onion (8-10 nm, but containing 40% of xyloglucan as well as cellulose) and quince (2 nm cellulose core). Both of these forms of cellulose contained crystalline units of similar size, as estimated from the ratio of surface to interior chains, and the time required for proton magnetisation to diffuse from the surface to the interior. It is suggested that the onion microfibrils must therefore be constructed from a number of cellulose subunits 2 nm in diameter, smaller than the 'elementary fibrils' envisaged previously. The size of these subunits would permit a hexagonal arrangement resembling the cellulose synthase complex.

Location and age of Mesolithic coastal occupation sites on Oronsay, Inner Hebrides.

The existence of at least five Mesolithic occupation sites on the island of Oronsay, Inner Hebrides, has now been established. Preliminary results of recent excavation of two of the sites were reported in 1971 (ref. 1). Since then further excavations have been made and the locations and ages of the sites in relation to the position of the shore line of the sea at the maximum of the Holocene marine transgression have been investigated. The results obtained suggest that the ages of some of the sites in relation to the former shore line cannot be established solely on stratigraphical and altitudinal evidence but require supplementary information based on radiocarbon dating. It will be some time before the full details will be published, and so a short account of the results so far obtained is presented now.