ARABLE WEEDS. ASSOCIATION WITH CROPS 163 



The plants in Table X are commonly associated with 

 every type of crop, and some of them are among the most 

 frequent and abundant weeds. A few of them, however, are 

 more specially favoured by certain crops, this being shown by 

 their relative abundance and the number of times that they 

 usurp the position of dominant weeds. Charlock (Brassica 

 sinapis] is often dominant among all crops, but particularly 

 in wheat and oats. Field bindweed (Convolvulus arvensis) 

 dominates very frequently, specially among barley and on 

 fallow land. Creeping thistle (Cirsium arvense), on the other 

 hand, is abundantly dominant among all crops, if allowed, but 

 it is rather less favoured by wheat, oats and seeds. The rest of 

 the weeds in this class are not often present in great quantity, 

 partly because they are so steadily eradicated when seen that 

 they do not have a fair chance. Sheep's sorrel (Rumex aceto- 

 sella] and groundsel (Senecio vulgaris) flourish best among 

 seeds ; corn sow-thistle (Sonchus arvensis] is seldom very 

 plentiful except with barley ; field speedwell ( Veronica agrestis] 

 is sometimes abundant among oats and peas and beans. Some 

 of the weeds, again, are frequently present in very small 

 quantity although they are so wide spread. Shepherd's purse 

 (Capsella bursa-pastoris) is often scarce among all crops, yellow 

 toadflax (Linaria vulgaris) is rarely or never dominant, while 

 the curled dock (Rumex crispus) is so persistently attacked 

 that it is rarely allowed to take first place among the weeds 

 and is instead often reduced to a position of scarcity. 



It is obvious that most of the weeds that are well 

 distributed among all crops are specially adapted for the 

 purpose, being able to tide over adverse circumstances in- 

 duced by the habit of any crop or by any particular method 

 of cultivation. Charlock, shepherd's purse, curled dock and 

 field speedwell produce large quantities of seeds which do not 

 all germinate at the same time. Some of these seeds start 

 into growth and the seedlings are often destroyed by cultiva- 

 tion, but another batch of seeds is waiting its turn, and 

 usually weeds of this description baffle the farmer unless 

 he is particularly alert. Creeping thistle and bindweed have 

 creeping underground stems which possess an amazing power 

 of retaining their vitality and growing under any circum- 

 stances, so that the type of crop does not affect them greatly. 

 Corn sow-thistle and groundsel are provided with plumed 

 fruits, and the seeds may not only remain buried in the soil 

 from one year to another, but a fresh supply may be constantly 



