A few additions to Lou's list of variables. I find that the best way for me to find variables is to travel and be startled by climate differences compared to my maritime home. A few that must have an effect on plants: the intensity of winter light in Arizona fog dripping off plants in summer in Tofino incredible night and day temperature differences in the Karoo - from minus 8 to plus 22 in one 12 hour period Diane Whitehead Victoria, British Columbia, Canada On 21-Nov-09, at 10:35 AM, lou jost wrote: > winter rains or summer rains > summmer temperatures are high or low > thick snow or not during the winter > climate is seasonal or constant > humid or dry > dew or not during the driest time;