Dormancy was broken completely during 24 weeks of incubation
at 15/5 C, but dormancy break was still continuing at 20/10 C.
At these temperature regimes, ngseeds were cold stratified at night
when the temperature was at 5 and 10 C, respectively, indicating
that effective cold stratification for Acer species is 10 C. Size of the
embryo in seeds of A. morrisonense did not change before radicle
emergence. However, length of the first true leaves on the epicotyl
plumule increased 300% during cold stratification for 12 weeks, and
newly-formed cells were observed in the plumular apical meristem
(Fig. S1, Appendix B) and in the first true leaves (Fig. 3f; Fig. S2,
Appendix B), indicating that cold stratification induced cell division
and plumule growth.