The Effect of Weeds upon Cereal Crops. 65 
Brassica is present in a wheat crop even in a moderate amount, it is 
capable of doing a great deal of damage, as the vigorous growth and 
the broad coarse leaves render it a much more formidable competitor, 
plant for plant, than many of the other weeds. 
Experiment 4, 1915. 
The Woburn soil used in the previous experiment was mixed 
with a fresh load, also brought from Woburn, and 48 pots were filled 
with the mixture. A corresponding set of 48 pots were filled with 
heavy Rothamsted soil from Stackyard field, mixed with 10% of sand, 
to make it more workable. In the previous tests the seeding of the 
pots had been similar and equal all through the series. This time 
it was decided to try the effect of both light and heavy seeding in 
order to ascertain whether the competition between plants of the 
same species is as severe as that between plants of different species* 
To this end the following scheme of seeding was adopted, six similar 
pots being the unit in each case. 
Wheat + Wheat. 
Wheat. 
Wheat + Weed. 
Weed. 
Weed + Weed. 
Seeds were sown on April 20th. The wheat seeds were 
counted and were dibbled in at regular intervals round the pots. 
The smaller weed seeds were weighed out, the larger were counted, 
and all were scattered broadcast in order to give the roots of the 
weeds a better chance of coming into direct contact with the wheat 
roots. The following quantities were sown per pot:— 
Single sowing. 
Wheat 8 seeds, thinned to 4. 
Papaver 0*015 gram. 
Spergula 0*045 gram. 
Alopecurus 20 seeds. 
Brassica 20 seeds. 
Double sowing. 
Wheat 16 seeds, thinned to 8. 
Papaver 0*030 gram. 
Spergula 0*090 grm. 
Alopecurus 40 seeds. 
Brassica 40 seeds. 
As before Spergula and Papaver were grown on Woburn soil, 
Brassica and Alopecurus on Rothamsted soil. 
A number of alien weeds came up from buried seeds, but 
these were frequently pulled up in order to leave a clear field for 
the experimental plants. A few big poppies appeared from buried 
seeds in the Woburn soil, but as their larger size easily distinguished 
these from those sown, they were pulled up as early as possible. 
