The Effect of Weeds upon Cereal Crops. 69 
rather earlier than the wheat, falls to the ground and germinates 
quite early in the autumn. If another white crop follows on, so that 
cultivation cannot be carried out, then the Alopecurus has a 
chance of establishing itself; if rotation is followed or spring corn 
is sown, it is easy to get rid of the pest. These facts indicate 
that this weed is particular in its demands, and that it grows best 
with autumn sowing and with those plants that give it a certain 
amount of shelter in its young stages. This may account for the 
individual plants in the single pots being so much poorer than in 
the double pots—possibly the stand is too thin to provide the 
necessary shelter and so development fell behind. 
The wheat behaved as usual—the plants with single sowing 
and with the weed that failed were individually much the same 
and were very much heavier than those sown more thickly, though 
they did not attain to quite twice the size. Under the conditions 
of experiment the wheat was a fatal competitor to the Alopecurus , 
though it suffered no check itself from the competition of the 
weed. 
Wheat and Brassica. 
Thinly sown Brassica , grown alone, made more individual 
growth than that sown thickly. In the presence of wheat, how¬ 
ever, a marked fall occurred, and the individuals only made about 
half the growth of those in the double pots ; i.e., in this case, other 
things being equal, the competition between wheat and Brassica 
was greater than that between the Brassica plants themselves. The 
wheat, on the contrary, made better growth with Brassica than in 
the double sown pots, so that the effect of the Brassica on the wheat 
was less than that of the wheat itself. 
Experiment 5, 1916. 
The soil from each pot used in the 1915 experiment was tipped 
out, thoroughly mixed up and returned to the same pot. The same 
species and quantities of weeds were used as in the previous experi¬ 
ment, and they were sown in the same pots in the way previously 
described, so that Papaver followed Papaver and crop -\-Spergula 
followed crop -\-Spergula, and so on. Owing to a deficiency in supply 
only 11 Alopecurus seeds could be used for a single sowing, 
instead of 20, and also barley was used as the crop plant instead 
of wheat to get over the difficulty arising from the unavoidable 
lateness of sowing. As usual two barley seeds were sown per 
clump and thinned soon after the seeds had germinated. The 
