THE 
HEW PflYTOItOGIST. 
Vol. XVI, Nos. 3 & 4. March & April, 1917. 
[P ublished May 8th, 1917.] 
THE EFFECT OF WEEDS UPON CEREAL CROPS. 
By Winifred E. Brenchley, D.Sc. 
(Rothamsted Experimental Station). 
O NE of the great problems with which a farmer has to deal is 
the presence among his crops of weeds or plants other than 
those sown, which are inimical to the obtaining of maximum results. 
It is impossible to sow any crop without the certainty that other 
plants will appear, derived either from seeds already buried in the 
soil or from alien seeds introduced with the crop. The practical 
results of the competition of weed and crop are well known, but 
the exact cause of this competition is less obvious. The weeds 
utilise food and water from the soil, and above ground they tend to 
shade the crop and rob it of much of the sunlight essential to full 
development. The question constantly arises, however, as to 
whether this mere “ vegetative competition,” if it maybe so termed, 
is the only factor at work, or whether the weeds excrete from their 
roots some poisonous substance which actively inhibits the growth 
of the crops. Fletcher 12 has carried out various experiments in 
India and Egypt and maintains that some species are actively 
injurious to others owing to toxic excretions from the roots. The 
fruit farm experiments at Woburn indicate that growing grass round 
fruit trees is harmful to the growth of the trees, but Dr. E. J. Russell, 3 
in discussing various experiments on the subject, indicates that if a 
toxic substance is excreted, it is extremely unstable, and “ changes 
into something which is harmless, or may even be beneficial to 
plants,” and that “ certain experiments made at Rothamsted by 
1 Fletcher, F., 1908. Memoirs of the Department of Agriculture in India. 
Vol. II, No. 3 (Bot. Ser.). 
1 Ibid, 1912. Toxic Excreta of Plants. Journ. Agric. Science, Vol. IV, 
pp. 245—247. 
3 Russell, E. J. Effect of one Growing Crop on Another. Report XIV, 
Woburn Experimental Fruit Farm, pp. 63, 66. 
