156 Brenchley . — The Weeds of Arable Land. III. 
In a recent study on the purity of agricultural seeds Borlase 1 gives the 
following weed seeds as commonly occurring as impurities in samples 
of clover and other leguminous seeds : 
Bromus mollis 
Caucalis Anthriscus 
Festuca bromoides 
Geranium dissectum 
„ molle 
Lychnis alba 
Plantago lanceolata 
Poa annua 
Prunella vulgaris 
Rumex Acetosella 
„ crispus 
Sherardia arvensis 
Chrysanthemum leucanthemum, Rumex Acetosa, and Lychnis diurna are 
also occasionally found. It appears that Geranium dissectum is the species 
of Geranium commonly associated with Red Clover seeds, while Geranium 
molle is found among Alsike and White Clover seeds. With regard to 
cereals and roots Borlase states that ‘ in the former there are very few weed 
seeds, as their presence would be easily detected owing to differences in size 
and colour, and with the latter difference of shape and colour would reveal 
most to the naked eye \ He also quotes two samples of weeds introduced 
with imported seeds which have established themselves as serious pests 
in parts of Cornwall. Bromus secalinus is a bad best in the Winter Oat 
crop, but in no other, and may have been introduced from Canada, where it 
is common and is known as ‘ Cheat \ Matricaria suaveolens was introduced 
into Cornwall about fifteen years ago from North Asia or Western North 
America, and is now so prevalent in some places that it absolutely destroys 
the corn crops. 
It is now evident that while the soil is the primary determining factor, 
still the nature of the crop plays a larger part than was originally supposed. 
While this influence is partly due to the different habits of the crops, 
it is probably more the result of the varying methods of cultivation applied 
to the crops. Broadly speaking, a four-course rotation is usually followed in 
the district studied : 
(1) Wheat. 
(2) Roots. 
(3) Barley or oats. 
(4) Seeds and leguminous crops. 
With the seed crops nothing can be done to keep the land clean, so the 
weed flora among the ensuing wheat tends to be specially fruitful in the 
varieties occurring in the young corn, though if the crop is very heavy 
it tends to strangle many of the weeds later on, a fact that is usually 
attributed to the exclusion of light and air. With the root crops comes the 
1 Borlase, W. : The Study of Agricultural Seeds. Journ. Board. Agric., xix, No. 7, pp. 529-41. 
I am also indebted to Mr. Borlase for a private communication in which he gave me much of the 
information in this paragraph. 
