contra-selection

Updated: May 29, 2025

I got figures of 90% and above, coming even in one instance up to the apparent purity of 100%. These, however, always remained extremes, the averages fluctuating yearly between 80-90% or thereabouts, and the other extremes going nearly every year downwards to 50%, the value which would be attained, if no selection were made. Contra-selection is as easily made as normal selection.

Hugo de Vries - Species and Varieties, Their Origin by Mutation

But to transgress this average on the lower side seems to be as difficult as it is on the upper side. I continued the experiment during four succeeding generations, but was not able to go lower than about 10%, and could not even exclude the high figures from my strain. Parents with 65-75% of syncotylous seedlings returned in each generation, notwithstanding the most careful contra-selection.

Hugo de Vries - Species and Varieties, Their Origin by Mutation