30 Buried Weed Seeds 



Park Grass, allows of the ripening of the seeds of many species in a differ- 

 ential degree, the earlier species having a better chance than those which 

 flower later in the season. Consecjuently far more seeds become buried in 

 this case, and the flora tends to remain very varied. 



A striking difference exists between the buried seed flora of permanent 

 grassland and of land that has at one time been under the plough, even 

 though nearly 60 years have elapsed since grassing down. The permanent 

 grassland is largely colonised by species of grasses and miscellaneous 

 plants which are definitely associated with pasture and never with arable 

 land, except for the one or two arable weeds which must be of accidental 

 origin. On land that was originally arable however, a large number of 

 plants occur, such as hardhead, mouse-ear chickweed, ribwort plan- 

 tain, chickweed, etc., which are common to both arable and grassland, 

 indicating that when once these species are established on an area they 

 can persist, even when the type of cultivation is changed. 



A fair number of true arable weeds appear even from soil that has been 

 grassed over for 58 years (Laboratory House Meadow) and, as was shown 

 in the special discussion above, many of these may almost certainly be 

 regarded as survivors from seeds left in the soil from the time of arable 

 cultivation. The pro])ortion of grassland plants is large compared to that 

 of the arable weeds, a result that is in complete accordance with expec- 

 tations. Geescroft field has been under grass for a shorter period of time, 

 and the number of arable seeds is greater, while the proportion of grass- 

 land plants has decreased. This trend of events becomes more marked 

 as the time of grassing down gets less, and on New Zealand field, with only 

 10 years under grass, the arable weeds bear a heavy proportion to the 

 grassland plants, particularly if the clovers (which might have been de- 

 rived from buried seeds of a sown crop) are left out of consideration. 

 The transition from the state of affairs on such temporary grassland to 

 that on ordinary ploughed land is gradual and in the same sense, the 

 number of arable weeds being greatly increased, the arable or grassland 

 plants being sparsely represented, while the true grassland plants are 

 almost absent. 



The changes in the proportion of the arable and grassland plants de- 

 rived from buried seeds are so consistent and so regularly associated with 

 the history of the land that one is irresistibly forced to the conclusion 

 that when arable land is grassed over a certain number of the seeds are 

 able to retain their vitality for very many years. Many of the seeds die 

 within a comparatively short time after burial, and as time goes on the 

 number of living seeds gradually becomes less, though the evidence goes 



