Second,although tight climate control sounds highly desirable, it may simultaneously reduce the so-called ‘external validity’ of the results (Richter et al. 2009). That is, by making the conditions highly specific, reproducibility across laboratories may actually decrease, with the result that generalisations are less easily made.Richter et al. (2009), therefore, advocate the use of a range of subplots within the experiment where plants are grown and measured at somewhat differently designed conditions. One useful experimental design in this respect is to undertake an
experiment concurrently in more than one growth chamber,glasshouse or experimental garden using nested treatments
within each replicated facility. In the end, repeating the experiment in time is probably the best way to filter out many
spurious results.