Brenchley.~The Weeds of Arable Land. III. 1 6 1 
Scrophulariaceae is very much to the fore with the genera Veronica 
and Linarm, both of which yield several species, the Veronicas being among 
the most common of weeds. Cruciferae and Caryophyllaceae are each 
represented by several genera with about one species from each as a rule, 
though the genera Brassica (Cruciferae) and Lychnis and Silene (Caryo- 
phyllaceae) are very rich in their contribution of species. Polygonaceae, 
again, is particularly well marked with several species of Polygonum and 
Rumex , which have the doubtful distinction of being among the commonest 
and worst weeds from the farmer’s point of view. Graminaceae yields a fair 
number of species from different genera, but the weed order is undoubtedly 
Compositae so far as the number of representatives is concerned, for at 
least half the British genera of this large order contribute one or more of their 
species to the weed flora. The distribution of the Compositae, too, is very 
wide, both as regards the soils and crops with which they are associated. 
The analyses indicate that the cultivated fields provide a definite 
ecological habitat, which is differently adapted to the support of the various 
great families of plants. 
2. Different species of the same genus are often distinctive in the type 
of soil they characteristically inhabit, as the following well-marked instances 
show : 
Anthemis arvensis 
sandy soils and chalk 
„ Cotula 
loam 
Carduus nutans 
calcareous soils 
„ arvensis 
distributed 
Chrysanthemum Leucanthemum 
loam 
„ segetum 
sand 
Euphorbia exigua 
heavy loam and clay 
„ Helioscopia 
calcareous soils 
„ Peplus 
loam 
Geranium dissectum 
heavy loam and clay 
,, molle 
light and chalky soil 
,, pusillum 
33 33 33 33 
Linaria Elatine 
heavy soils 
„ minor 
sandy soils 
„ vulgaris 
calcareous soils 
Polygonum aviculare 
distributed 
„ Convolvulus 
loam and sand 
,, Lapathifolium 
sand 
„ Persicaria 
light sandy soils 
Ranunculus acris 
loam 
„ arvensis 
heavy loam and clay 
„ repens 
distributed 
M 
