Flax has been selected for two different economic characteristics of yield, fiber and oil. These two forms are phenotypically different and have different agronomical practices associated with their cultivation. In particular, the plants for the fiber crop are grown at a high density. It has been observed for many centuries that subsequent generations of plants grown from seed of the fiber crop show rapid variations in phenotype in spite of the plants essentially being self-fertilizing and homozygous. One possibility for these observations was that the vigor of the seed from the fiber crop was reduced through the generations due to the restriction of available nutrients by the high-density plantings. This hypothesis was examined by Durrant by growing plants with various nutrient regimes and determining the phenotypes following repeated identical treatments or after a succession of different growth environments. It was observed that for a small number of nutrient regimes, some fiber flax varieties had a heritable change in their phenotype, irrespective of their subsequent growth environment. These stably altered inbred lines were termed genotrophs, as at that time it was not known that they were genetically distinct genotypes. The relationships between the various lines, especially those derived from the original variety Stormont cirus, and the timing of when these changes occur, are described. Their molecular comparisons are considered in the next chapter.