Winifred E. Brenciilkv 31 



to show that some seeds will survive burial for at least 58 years. Usually 

 most of the older arable seeds survive in the lower depths of soil where 

 the conditions are less variable, whereas the shorter the time that land 

 has been under grass the greater the proportion of arable seeds that are 

 found near the surface. While the stock of arable seeds is diminishing 

 with the lapse of time, the supply of grassland seeds is being augmented 

 by the fresh seeds that are ripened by the surface vegetation and are 

 gradually carried down into the soil. Naturally enough, the greater 

 number of these seeds are found in the upper inches of soil, comparatively 

 few penetrating below the eighth inch. 



Such fields as Barn Field Arable and Agdell show clearly how close 

 is the connection between the methods of cultivation and the supply of 

 weed seeds that become buried in the soil. Continual cultivation for 

 roots, as on Barn Field, keeps most of the weeds from seeding and so pre- 

 vents the accumulation of large stores of seeds in the soil. On the Agdell 

 plot it is probable that many of the weeds have become starved out, or 

 so impoverished that their seeds are not strong enough to survive for any 

 length of time. Neither of these instances, however, is at all normal, as 

 they are the result of experiment and not of ordinary farm management. 



From consideration of the results of the above experiments it may 

 be concluded that the case for large crops of charlock, poppies or other 

 arable weeds appearing when real old pasture is ploughed up must 

 still be regarded as not proven. These particular weeds were not 

 obtained in the soil from old pastures, nor were they present when the 

 land had been under grass for nearly sixty years. Nevertheless it is 

 evident that under suitable conditions the seeds of some weeds are able 

 to lie dormant at various depths in the soil over long periods, and to 

 start into activity if and when the method of cultivation is so changed 

 that they are brought nearer to the surface into the presence of the 

 right combination of warmth, air and moisture. Consequently, the large 

 crops of weeds that appear when temporary pasture is ploughed up 

 must be regarded as being derived from seeds buried in the soil, and 

 not from seeds transported from other areas by external agencies. 



(Received October 8th, 1917.) 



