Thanks for your observation, Ashley. All this stems from a snippet of information remembered from a talk I attended on snowdrops in their native habitats. It was stated that in the case of the autumn-flowering reginae-olgaes, plants growing on the shady side of a rock came into flower sooner so the inference was made that is was the reduction in temperature that triggered the flowering. Whether any of this translates to our much cooler latitude or to elwesiis are moot points.