159 
Brenchley . — The Weeds of Arable Land . ///. 
Artemisia vulgaris 
Carduus nutans 
Linaria minor 
Raphanus Raphanistrum 
Silene gallica 
In all probability this selectivity is the result of some peculiar adapta- 
tion to the particular cultural conditions of the associated crop. This 
association with particular cereal crops is, however, not yet proved 
universally. So far as the species correspond, there is a fairly close agree- 
ment between the Bedfordshire and Norfolk results, but in the West 
Country some species, as Alopecurus myosnroides , Heracleum Sphondylium , 
Chrysanthemum segetum , are associated with wheat, barley, and oats instead 
of being chiefly found with wheat as they are in the Eastern Counties. This 
may prove to be due to differing local customs with regard to the growing 
of Spring or Winter Oats, but information on this point is not immediately 
available. 
When the tabulated results for the three years are placed side by side 
and compared, it is seen that certain of the weeds are always to be found in 
association with all types of crop in the different districts. Other species 
are apparently more variable — perhaps they are rather more sensitive 
to differences of local conditions —and so while they may be associated with 
every type of crop in one place, they may be absent from one or other 
of the crops in another district. A few plants are much more rigid in their 
adherence or aversion to some particular crop. For instance, the following 
plants have been frequently observed in each of the three seasons, and 
consistently they have been found to be either absent or very rare among 
root crops : 
Anthemis Cotula Ranunculus acris 
Bartsia Odontites „ arvensis 
Cerastium vulgatum Taraxacum vulgare 
Plantago lanceolata 
This probably indicates that these plants are particularly impatient 
of interference, and so they find a position among the root crops untenable 
on account of the repeated cultivation carried on. 
Again, some other species seem to be quite unable to cope with the 
keen competition for light, and possibly for air, that occurs among the seed 
crops, as is indicated by the rarity with which the following are found in 
such surroundings : 
Agropyron repens Poa annua 
Gnaphalium uliginosum Veronica hederaefolia 
Legousia hybrida 
never with wheat ; always with 
barley or oats. 
