WEEDS— PECULIARITIES AND DISTRIBUTION 429 



to hand-hoe the barley in order to save the crop. In 1910 the 

 weed was very abundant but further search in 191 1 revealed 

 very few specimens of the plant, illustrating the great part 

 that seasonal conditions play in affecting the prevalence of 

 weeds. The Wild Pansy {Viola tricolor) is another noticeable 

 species on chalk, though it is hardly symptomatic. This is a 

 most variable plant, the flowers varying in size from tiny, 

 insignificant things to fine specimens half an inch or more 

 across, whilst the colour grades from white to deep blue. The 

 suggestion has been made that the blue coloration indicates 

 a substratum rich in nitrogen and that the paler the colour 

 the less is the amount of available nitrogen present, so that 

 the white form affords an indication that the soil is more or less 

 deficient in this essential plant-food ; this suggestion, however, 

 awaits confirmation. 



In Wiltshire the Shepherd's Needle {Scandix pecten) is a most 

 noticeable feature on the chalk, especially on the heavier red 

 land lying towards the top of the downs ; the plant is a member 

 of the order Umbelliferae, its name being assigned to it on 

 account of its big needle-like fruits which are ridiculously 

 out of proportion to the minute, insignificant flowers which 

 precede them. In some instances this weed is dominant, being 

 present in very great abundance. 



The Scarlet Pimpernel (Anagallis arvensis) and Fat Hen 

 {Chcnopodium album) provide further instances which show how 

 differently one and the same species may behave on similar 

 soils in different parts of the country. Both these plants are 

 absent from the chalk soils in Bedfordshire, so much so that 

 they were regarded as lime-haters. In Wiltshire Fat Hen is 

 recorded more frequently from chalk than from an}' other 

 habitat, whilst the Pimpernel is universally found on the 

 chalk (in addition to other localities), although only very small 

 quantities of it appear in such situations. 



Whilst so many species of weeds can be associated with 

 definite soils, there are a large number which are quite univer- 

 sally distributed, occurring on all types of soil ; these may be 

 dominant on any soil. This set of weeds include many of the 

 very common species, those which are known to every one. 

 Indeed, perhaps it is because of their universal distribution 

 that they are so well known. Many of these, in addition to 



