ARABLE WEEDS. ASSOCIATION WITH SOILS 133 



(3) Willow-weed (Polygonum persecaria) stands apart from 

 all other weeds in its habits and habitats. It is most intoler- 

 ant of chalk, but otherwise seems indifferent to the nature of 

 the soil. Sometimes it behaves like other weeds and is spread 

 more or less evenly over the fields, or is segregated in areas 

 that are determined by definite and marked local conditions. 

 More usually, however, its distribution is sporadic. It occurs 

 here and there in spots,' sometimes at the bottom of a field, 

 where the soil is moister, sometimes towards the top, where 

 no obvious difference in water content is evident. It is abun- 

 dant and usually dominant on peaty soils and grows happily 

 in parts of fields that are often waterlogged or are churned up 

 into thick mud by the farm traffic. When the plant occurs 

 high and dry towards the top of a field, inquiry will often elicit 

 the information that a spring emerges near by, or that at some 

 periods of the year those spots are extra damp from some 

 source of underground water. Careful consideration leads to 

 the conclusion that soil plays but a small part in determining 

 the distribution of willow-weed, but that a plentiful supply of 

 underground water is essential if the plant is to flourish. 

 Chalky soils are thoroughly well drained, and rarely have 

 sodden spots, so the absence of willow-weed from these situa- 

 tions may be due either to chalk intolerance or to a deficient 

 water supply. The weed is frequent enough on sand, and is 

 even sometimes dominant there, but sandy soils often have 

 damp soggy spots in which the plant can flourish, or the water 

 table may be sufficiently near the surface to enable the roots 

 to travel down to reach abundant moisture. 



On the heavy clay fields in part of Somerset, which are 

 low-lying and near the moors, willow-weed flourishes well and 

 spreads uniformly over the whole area, as the necessary con- 

 ditions of moisture are fulfilled everywhere, and not only in 

 isolated spots. 



Pale poppy (Papaver argemone) is seldom seen, either be- 

 cause it really does not occur, or because it is present in such 

 small quantities that it is overlooked or confused with other 

 larger species of poppy. It occurs anywhere except on chalky 

 soils, but is often scarce. 



Broad dock (Rumex obiusifolius) must be regarded as an 

 interloper among arable weeds. It seems to object strongly 

 to chalk or else it so happened that it had been cultivated out 

 of existence in every field visited during the course of the in- 

 vestigation. The plant is essentially a weed of waste places, 



