Adaptation to heterogeneous environments. II.* Phenotypic plasticity in response to spacing in Linum

Abstract

Six varieties of Linum usitatissimum, three of flax and three of linseed, were grown under field conditions at six different spacings, from 1 to 32 in. (2.5–81.3 cm) apart. There was abundant evidence of varietal differences in phenotypic plasticity in response to variation in spacing. This indicates that response to spacing is a genetically controlled and not an automatic phenomenon. The major differences were between the flax and linseed groups; linseed varieties were more responsive in branching. However, there were considerable differences between varieties within each group. Different characters showed very different patterns and degrees of response, which indicated that control of response operates on an individual character rather than on a whole organisms basis. Plausible explanations in terms of natural selection can be given for the origin of many of the differences in the response of varieties and in characters. Taken as a whole, the results suggest that there is precise genetic control of the epigenetic processes involved in the response of plants to spacing, and that evolution of different patterns of response can easily occur. _______________ *Part 1, Evolution, 22: 496-516 (1968).