18 Buried Weed Seeds 



seedlings were well distributed in the soil from each of the four sampled 

 holes, indicating that the mother plants were probably common over the 

 field and were not localised in a few places. It is surprising that such a 

 large number of seeds have retained their germinating capacity for over 

 30 years and the survival of so many suggests that P. uvicularc was 

 exceedingly plentiful when the area was cultivated. The old Rothamsted 

 records show that this was actually the case and that knotgrass was one 

 of the worst weeds occurring among the crops. Plantayo inajor was also 

 very characteristic at that time and a numberof seedlings ap])eared during 

 the present experiment, but as this species is common to both arable 

 and grass land and still occurs in the field, it is not possible to ascertain 

 the length of time the seeds had been buried in the soil. Those occurring 

 in the upper layers of soil are nearly certain to be of comparatively 

 recent date. None of the typical arable weeds that appeared in the soil 

 samples are to be found in the surface vegetation of the field nowadays, 

 whereas they were all recorded as being present among the crojJS in 1867, 

 a fact which renders it still more probable that the seedhngs obtained in 

 the experiment grew from seeds which had been buried in the soil at 

 least since the land was thrown into the Park in 1885. 



A large number of typical grassland seedlings appeared and also a 

 certain number of species that are common to both arable and grassland. 

 The greater number (T-'j %) of the grassland seeds were present in the top 

 four inches of soil, whereas most of the arable seeds (68 %) were found 

 from five inches to nine inches below the surface. The stock of grassland 

 seeds is replenished year by year as the plants on the surface ripen their 

 fruits, so that it naturally happens that the bulk of the youngest and 

 most viable seeds occur near the surface. As the seeds get carried down 

 into lower depths in the course of time many of them lose their power 

 of germination with increasing age, and the lowest inches contain very 

 few seeds that are capable of growth when the soil is disturbed. On the 

 other hand the long-buried arable seeds have apparently found some 

 conditions of equilibrium in the middle depths which have enabled them 

 to remain unharmed all these years. When the land first passed out of 

 cultivation the greater number of arable weed seeds must have been in 

 the top few inches. The conditions of aeration, temj^erature and moisture 

 down to a depth of three or four inches at least, are such as to induce 

 germination, which is effective or incipient according to the variety of 

 seed concerned and the depth at which it is buried. Consecjuently in the 

 course of the first few years most of the seeds towards the surface died 

 off, either by germination or by rotting. The more deeply buried seeds. 



