thaw <- read.table("thaw.dat",header=T)
thaw$code <- thaw$regime + 2 * (thaw$temp - 1)
thaw$regime <- factor(thaw$regime)
thaw$temp <- factor(thaw$temp)

thaw.ifit <- lm(ion ~ regime * temp, thaw)
thaw.pfit <- lm(photo ~ ion + regime * temp, thaw)
thaw.afit <- lm(photo ~ ion + regime + temp, thaw)

thaw.lfit<-lm(log(2 + ion) ~ regime * temp, thaw)