39 



or charlock than it did from the same number of barley plants, whereas 

 black bent was not nearly as powerful a competitor. 



So far as could be seen^ however, the effect was solely one of com- 

 petition for food, and it made no difference to the individual wheat 

 plant whether its competitor was another wheat plant or a plant of 

 some wholly different order. The phenomena could all be explained 

 by supposing that the number of plants the soil could carry depended 

 on the amount of food present in the soil and the amount of space 

 available for growth ; if the food and space are to be shared by many 

 plants each individual will get a smaller share and therefore make less 

 growth than if there are fewer plants to participate. 



XXXI. "Buried Weed Seeds." Winifred E. Brenchley. 

 Journal of Agricultural Science, 1918. 9, 1-31. 



A number of samples were taken from different grass fields by means 

 of a sampling iron, 6 inches by 6 inches by 9 inches. This was driven 

 into the ground, and the soil was carefully removed inch by inch, each 

 inch being placed in new paper bags and carefully labelled to indicate 

 the depth from which it was taken. The iron was driven far enough in 

 to permit of sampling to a depth of 12 inches, and special precautions 

 were taken that no crumbs of soil from the surrounding areas fell inside 

 the sampling iron. The samples were then placed in clean sterilised 

 pans or boxes in a glasshouse, kept watered, and left undisturbed for 

 a time. Seeds soon began to germinate, and as soon as the young 

 plants were large enough to be recognised they were noted and removed 

 from the soil. 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 buried seeds of permanent grassland include 

 species of grasses and miscellaneous plants which are definitely 

 j'/isociiitcd with pasture and never with arable land. Land that was 

 originally arable, however, contains a large number of buried seeds, 

 suc'i cs, Centaurea nigra, Cerastium vulgatum, Stellaria media, Plantago 

 lanceokUa etc., which are common to both arable and grassland. This 

 may indic.i,tc that these species are really arable weeds, but being able 

 to accommodate themselves to grassland conditions they can persist 

 wh'ja once tlicy are established on an area, whether the cultivation be 

 r.rcibK; or p;\sture. 



A f.ur number of true arable weeds appeared from soil tha-; has been 

 grossed over f« r 58 years (Laboratory House Meadow), many of which 

 may certainly be regarded as survivors of seeds left in the soil when it 

 was und -x arablo cultivation. The proportion of grassland plants, 

 however, is large compared to that of the arable weeds. Geescroft has 

 been under gmss for a shorter period of time, and the number of arable 

 s^eds is greater, while the proportion of grassland seeds has decreased. 

 This tendency becomes more marked as the period in grass becomes 

 L'ss, a-.d on New Z-ji.land field, only ten years under grass, the arable 

 weeds bear a heavy proportion to the grassland plants, particularly if 

 ■ th'j clovers (which might have been derived from buried seeds of a 

 sown crop), are left out of consideration. 



Tae cha iges in the proportion of the arable and grassland plants 

 derived from buried seeds a:-e so consistent and so regularly associated 

 with the history of the lard that one is irresistibly forced to the con- 

 clusion tha :, when arable land is grassed over a certain number of seeds 



