Mature seeds of Norway maple (Acer platanoides L.) are tolerant of desiccation, at least to moisture contents of about 7% (fresh weight basis), but those of sycamore (Acer pseudoplatanus) are killed by drying below about 45% moisture content. Sycamore seeds are thus recalcitrant; while the classification of those of Norway maple as orthodox is confirmed by the fact that between 19% and 7.5% moisture content their longevity is increased in a predictable way by reduction of seed moisturecontent. However, the period of useful storage of the latter in seed banks may be much less than for many crop species. The rates of water loss to a dry environment of both fruits and seeds of sycamore are much less than those of Norway maple, suggesting a degree of desiccationavoidance in the desiccation-intolerant species. Seed physiological maturity (maximum dry weight) occurred 2–3 weeks earlier in Norway maple than insycamore, but in both species this occurred about 150–160 days after peak flowering. Tetrazolium staining is a good indicator of embryo viability in both species, correlating well with germination test results. In Norway maple both methods of viability testing indicated that whole-seed desiccation tolerance coincided with the attainment of maximum dry weight. Tetrazolium staining indicated the development of desiccation tolerance in the radicles/hypocotyls of both species approximately 2–4 weeks before physiological maturity. Possible correlation between changes in the level of embryo dormancy during development and the acquisition of desiccation tolerance are discussed.

The viability of Norway maple seeds collected 21 d before mass maturity (68%moisture content, wet basis) and at mass maturity (56% moisture content) was reduced from 52–85% to 0–7% if dried rapidly (at 10–12% r.h. and 15–17°C for 3 d, then 3 d over silica gel) to 4–5% moisture content. Moist storage of the fruits at 15°C improved the ability of the seeds to tolerate rapid desiccation considerably: 10 and 21 d of moist storage enabled seeds collected at mass maturity or 21 d earlier, respectively, to attain maximum desiccation tolerance to 4–5% moisture content. Moist storage and/or subsequent desiccation affected stachyose, sucrose, and to a lesser extent raffinose, concentrations. The oligosaccharide:total sugar ratio showed a similar pattern in relation to ability to germinate after desiccation to 4–5% moisture content among seeds collected on both dates: desiccation tolerance developed from nil to maximal in these seed populations between threshold oligosaccharide:total sugar values of just less than 0.3 and about 0.4.