A temperature-dependent source of variability in estimates of germination behaviour of lettuce fruits.

Germination of fruits of Lactuca sativa L. cv. "Arctic King" showed a sharp upper temperature maximum at 31±1.0°C on an agar substrate in light. In a series of 60 tests carried out over 2 years, above, below and in the region of this maximum it was demonstrated that variability of germination counts was greater in the transition zone around this maximum. This is important when single controlled temperatures are chosen to compare effects of chemical or physical stresses on germination, where the stress causes the transition zone to shift and introduces a factor of greater variability into the results.