ARABLE WEEDS. ASSOCIATION WITH SOILS 119 



proportion so that a series was obtained containing , , , I 

 and twice the amount of chalk really required. Various seeds 

 were sown, including grasses, Rumex acetosa, R. acetosella, and 

 Trifoliuni pratense, and in addition a mixture of all the seeds 

 was made and sown in big pots prepared with soil similar to 

 that in the small pots. The plants were all kept under the same 

 conditions in a glass house and were carefully watered. At 

 the close of the experiment the plants were cut, weighed 

 green, dried thoroughly and weighed again. It was found 

 that by far the heaviest crop of Rumex acetosa was obtained 

 from the pots that received twice as much chalk as was needed, 

 and that the weight of the crop was rather less in the more 

 acid soils than in those pots which had received a complete 

 dressing of chalk, thus disproving the statement that sorrel 

 prefers an acid soil to one containing a sufficiency of lime. 



Rumex acetosa. 



The sheep's sorrel germinated very badly in all the pots 

 and only one or two plants grew at all. The only pots in 

 which any fair amount of growth was made were two which 

 had received f and a full supply of lime, thus again showing 

 that this species will grow well on soils which are not acid. 



All the other species grown alone made satisfactory growth 

 in the soils of varying acidity, as, owing to the absence of 

 competition, they were able to make the most of the soil even 

 though it were not really very congenial. In the big pots, 

 on the other hand, the proportions of the various species varied 

 with the acidity, indicating that directly competition came into 

 play the plants that were most favoured by their particular 

 soil gained the upper hand, while the species that were more 

 indifferent suffered by the crowding of the other plants and 

 consequently developed less strongly. 



The explanation of the discrepancy between the results of 

 these pot cultures and the ordinary field observations probably 

 lies in the mere fact of the varying conditions of competition 

 between the plants. Acid conditions of soil are not particularly 



