VITALITY OF WEED SEEDS 83 



power of germination longer than those kept in dry storage or 

 those on the surface of the soil are still rather obscure. The 

 question is complicated and probably depends upon a certain 

 balance being reached between the various physiological con- 

 ditions in which the seed finds itself. The temperature is 

 more equable some inches below the surface of the soil, and 

 while seeds near or on the surface may perish from cold during 

 the winter, buried seeds do not usually suffer from extreme cold. 

 Strong sunlight may also be very injurious to germination, and 

 this again is ruled out 1 The stage of maturity is another 

 important factor. Immature seeds soon perish, but mature 

 and properly ripened seeds contain just enough water to 

 enable them to lie dormant, and the conditions of air and 

 moisture surrounding them in the soil seem to be such as to 

 enable them to mark time without undergoing further desicca- 

 tion or other vital changes. When once the long buried seeds 

 are brought to the surface they are likely to start into growth 

 very quickly. Experiments have shown that many species of 

 seeds that have been kept in unfavourable circumstances 

 germinate rapidly when the conditions are improved, 2 for in- 

 stance, when they are brought from prolonged darkness into 

 light. On the whole, the more deeply buried seeds retain 

 their germinating capacity the best, as was clearly shown by 

 the Rothamsted experiment above described and also by pot 

 experiments carried out by Dorph Petersen with various seeds 

 buried 3, 6, and 12 inches below the surface. 



Much more information and evidence are needed before it 

 will be possible to explain fully why large crops of certain 

 weeds, as charlock, poppies, and fireweed, spring up when land 

 is ploughed or cleared even when the weeds were not present 

 before the change of conditions. It is, however, quite clear 

 that in the majority of cases sufficient live weed seeds are 

 buried in the soil to supply far larger crops of weeds than any 

 farmer need desire. 



i 



1 Giimbel, H. (1912), Untersuchungen iiber die Keimungverhaltnisse ver- 

 schiedener Unkrauter, Landivirtsch. Jahrb., XLIII, pp. 215-331. 



2 Praktische Blatter fur Pflanzenbau und -schutz (1912), Summ. in Jour. Bd. 

 Agric., XIX, pp. 231-232. 



