154 Brenchley . — The Weeds of Arable Land. III. 
Urticaceae 
Graminaceae 
)> 
>> 
Polypodiaceae 
Urtica urens 
Aira caryophyllaea 
Alopecurus pratensis 
Bromus sterilis 
Poa pratensis 
Pteris aquilina 
sand 
>5 
light loam 
heavy loam 
loam 
sand 
Comparison of the Weed Flora of Norfolk with that of 
Bedfordshire and the West Country. 
The general aspects of the weed floras are more or less comparable as 
regards the distribution of the plants, but the number of the species occur- 
ring is considerably greater in Norfolk, partly because of the greater 
diversity in the soil and partly on account of the larger area covered by the 
investigation. Some few of the weeds are proving to have a real association 
with definite types of soil, while yet others show decided local differences in 
their distribution, being absent in one place from the very soil on which they 
are frequent or even characteristic in another locality. The question as to 
calcifuges can hardly be reopened at present, as so little chalk land was 
examined in Norfolk that the data is too meagre. Just one plant, Poa 
annna , stands out conspicuously in that it is the only plant that has proved 
to be consistently absent or very rare on chalk in each of the three districts. 
On the whole there is a closer correspondence between the weed floras 
of Norfolk and Bedfordshire than between that of the West Country and the 
Eastern Counties, both as regards distribution and the actual species found, 
a fact which may be due to the geographical proximity and to a closer 
approximation in the nature of the soils in the east. 
The most outstanding features of distinction and similarity are : 
i. Certain species are definitely associated with sand, always choosing 
that as a habitat in every locality : 
Chrysanthemum segetum Sisymbrium Thalianum 
Rumex Acetosella Spergula arvensis 
Scleranthus annuus 
Brassica arvensis , on the other hand, shows a consistent dislike of 
sandy soils. This is borne out by the work of Verhulst , 1 who states that his 
researches show that no affinity exists between Sinapsis arvensis ( Brassica 
arvensis ) and light soils. He finds Brassica arvensis to be characteristic of 
chalky soils and calcareous clays, while Raphanus Raphanistrum is confined 
to sand, clays, and non-calcareous muds, though where the nature of the soil 
1 Verhulst, A. : Quel est le vrai charactere biologique du Raphanus Raphanistrum , L., et du 
Sinapsis arvensis , L. ? Bull. Soc. Roy. Bot. Belgique, 48. 4. 1911, pp. 248-56. Abst. in Bot. 
Centralb. Band cxx, No. 12, p. 317. 
