The effect of constant and fluctuating temperature on the germination of the weed seeds in arable soil

1. Comparison between the germination of weed seeds from field soil which was first washed on a fine sieve with that which was left untreated showed that the washing process had no material effect on the germination of the species present. 2. Germination of all species was very definitely inhibited if the soil was kept in a cellar or incubator where the daily fluctuations in temperature were very slight and the light wholly or partially excluded. 3. Some weed seeds were more adversely affected by the conditions in the cellar and incubator than others, Alopecurus agrestis being the least and Papaver rhoeas the most sensitive of the more important species encountered. 4. The inhibiting effect of the conditions in the cellar and incubator is attributed to the lack of sufficient fluctuation in temperature, rather than to the reduction in light intensity, though with certain species this also may have played a part in the results. 5. Removal of the soil samples to the glasshouse after 1 or 2 years in the cellar or incubator where few or no seedlings had appeared resulted in a rapid germination of a variety of weed seeds, showing that their failure to appear sooner was due to unfavourable conditions in the previous circumstances. 6. Too long an exposure to the conditions in the cellar or incubator resulted in a loss of seeds by death, the capacity for survival varying with the different species. Alopecurus agrestis, for example, generally failed to survive 1 year, whereas Alchemilla arvensis and Papaver rhoeas showed a viability extending to at least 2 years. 7. The reason for the seasonal periodicity in germination evinced by several species is discussed, but no conclusions are reached except that temperature conditions are apparently of great but not of sole importance.