The Effect of Weeds upon Cereal Crops. 61 
In both cases the presence of buckwheat almost killed out the 
weed, both poppy and Alopecurus being very poor .The buckwheat 
itself profited by the increased space available, and increased by some 
40%—50% in dry weight. It seems as though in this case the 
increase must be due to the removal of aerial competition, as the 
buckwheat roots are so fine and the pots were so large that it hardly 
seems possible that competition between the roots can have come 
seriously into play. 
SOIL B. TOTAL DRY WEIGHTS OF CROP IN SIX POTS. 
Shoot. 
Root. 
Crop. 
Weed. 
Crop + 
Weed. 
Grams. 
Grams. 
Grams. 
Brassica + Brassica 
20-6 
1-85 
270 
Buckwheat + Brassica 
4-5 
L8 
20-4 
Buckwheat + Buckwheat 
065 
29-2 
Buckwheat + Spurrey 
2-5 
1-75 
Spurrey + Spurrey 
3-9 
035 
AVERAGE DRY WEIGHTS OF SHOOTS. 
Crop. 
Weed. 
Per clump. 
Per single sowing. 
Per single sowing. 
Grams. 
Grams. 
Grams. 
Brassica + Brassica 
1.72 
1.152 
4.5 
Buckwheat +Brassica 
0.75 
0.284 
1.7 
Buckwheat + Buckwheat 
1.215 
4.8 
Buckwheat- 
-Spergula 
0.417 
Spergula + Spergula 
0.325 
Buckwheat and Brassica alba; Buckwheat and Spergula. 
In this lighter soil the buckwheat grown by itself shows a 
remarkable drop in the dry weight when compared with that in 
the heavier soil, from 100% to about 57%, although when grown with 
the weeds it reaches an almost equal development in both soils. As 
a result the actual weight of the eight clumps grown alone is 
considerably less than that of the four clumps grown in association 
with the weeds. No explanation of this can be put forward. 
Buckwheat and Brassica. 
The Brassica was the only weed that made thoroughly good 
growth at this late date ; it is one of those plants that apparently 
