VITALITY OF WEED SEEDS 79 



seeds had been buried for twenty-five years, and still retained 

 their power of germinating as soon as conditions became more 

 favourable. 1 



In farming practice the seeds of broomrape (Orobanche sp.) 

 are credited with the power of lying dormant for several years 

 and germinating in succession. This has been corroborated by 

 pot experiments carried out for a period of fourteen years, 

 which showed that broomrape seeds are able to retain their 

 vitality when buried in soil for eight years. 2 Other workers 

 give the period as at least ten years, the variation being prob- 

 ably due to differing conditions. 



From the practical standpoint the case is very clear that 

 many weed seeds have the power of remaining buried for a long 

 time without perishing, but in the absence of definite experi- 

 mental and historical evidence many fantastic ideas on the 

 subject have gained credence. With a view to obtaining some 

 definite facts a series of experiments have been carried out 

 with soil from the Rothamsted fields, of which the detailed 

 history for many years past is accurately known. 3 Old arable 

 fields were selected which had been grassed over for fifty-eight, 

 forty-three, thirty-two, and ten years, while Harpenden Com- 

 mon, Park Grass (a piece of old pasture that is known to have 

 been under grass for at least 300 years), and also a field that 

 has long been ploughed, were used for comparison. Samples 

 of soil, 6 inches square, were taken inch by inch to a depth of 

 12 inches, the utmost care being used to avoid contamination 

 from surrounding soil. These samples were placed in shallow 

 earthenware pans and boxes in a greenhouse, kept moist and 

 watched for about two years. As seedlings appeared they 

 were identified and removed to make way for later comers. 



As was to be expected a large number of the seedlings 

 were those of typical grass-land plants, derived from seeds from 

 the covering herbage. No idea could be formed of the age of 

 these, so they were perforce left out of consideration. The 

 " real old pasture " from the Common and Park Grass yielded 

 all told six seeds of typical arable weeds, whose presence could 

 readily be accounted for by accidental carriage on the feet of 

 horses, cattle, human beings, wheels, birds, etc. All the old 



1 Parkin, J. (1918), " Vitality of Gorse Seed," Nature, 2552, Vol. 102, pp. 

 65-66. 



2 Passerini, N. (1910), " Duration of Vitality of Seeds of Orobanche crenata," 

 Atti R. Accad. Econ. Agr. Georg. Firanze, 5, ser. 7, No. i, pp. 1-7. 



3 Brenchley, W. E. (1918), "Buried Weed Seeds," Jour. Agric. Set., IX, 

 pp. 1-31. 



