Staptedon . — On the Plant Communities of Farm Land. 173 
is not the rule. The influence of impurities on the communities at high 
elevations in Mid-Wales 1 has already been referred to, and probably 
accounts for the sporadic appearance of weeds such as Silene Cucubalus , 
Caucalis nodosa , Matricaria inodor a, Laps ana communis, and Galium 
Aparine in the arable land. It is now generally accepted that seeds of 
a great number of species can lie dormant in the soil for considerable 
periods ; and it has been shown elsewhere 2 that poor grass and clover 
samples contain the seeds of a number of weeds common to root and 
cereal crops, which on favourable soils and under the influence of tillage 
operations probably manifest themselves as considerable nuisances, and on 
unfavourable soils may give rise to sporadic appearances of unusual weeds. 
The communities studied both on the Cotswolds and in Mid-Wales 
appear to be somewhat different under roots, cereals, Vetches, and ‘ seeds ’, 
as is shown by the following brief synopsis. 
(a) Cereals and Roots. 
The communities under cereals in particular have been elsewhere (10) 
shown to exhibit a regular seasonal change. The flora found late in June 
and during July (when the straw is reaching its maximum height) includes 
relatively fewer ground annuals than is the case earlier in the spring, and 
more tall, straggling, and climbing plants such as Sonchus arvensis , Poly - 
gonum Convolvulus , and Convolvulus arvensis , and also plants the seed 
of which germinates later in the season, e.g. Aethusa Cynapium. 
The flora on the stubble after the corn has been harvested is often 
an exceedingly rich one, and is more or less a replica of that occurring 
in the seedling corn early in the spring. For the purpose of the present 
comparisons the communities found under cereals from March till the 
middle of June are considered as representative. 
Certain species appear to be rare under roots ; on the Cotswolds this 
is true of 
Ranunculus arvensis . Bartsia Odontites. 
Erophila verna. Plant ago media . 
Lychnis Githago. Poa trivialis. 
Under poor farming on some of the Mid-Wales soils, certain species, 
which are not normally common in the root crop elsewhere, may be fairly 
plentiful : 
Alchemilla arvensis . M atricaria inodor a. 
Beilis perennis . Plant ago lanceolata. 
Lap sana communis. Holcus lanatus. 
1 Will be discussed in greater detail when dealing with grass-land. 
2 See Stapledon, R. G. (12). 
