9§ 
THE ESSEX NATURALIST. 
The thanks of the meeting were accorded to Mr. Whitehead for his 
communication. 
The President then called upon Miss Winifred E. Brenchley, D.Sc,.» 
Botanist to the Rothamsted Experimental Station, who gave a lecture 
entitled “ Weeds and their relation to Soils and Crops,” which she illus¬ 
trated by an excellent series of lantern slides. Dr. Brenchley kindly fur¬ 
nishes the following resume of her address :— 
« 
WEEDS AND THEIR RELATION TO SOILS AND CROPS. 
A weed on arable land may be defined as any plant other than the 
crop sown, but on grass-land it may be either a plant of low feeding value 
or one that grows so luxuriantly as to crowd out more valuable species. 
Weeds do damage by robbing crops of food, water and light, and 
so reducing the yield, by adding expense to cultivation, by spoiling wool 
and seeds, and, in the case of parasitic weeds like dodder, yellow rattle and 
broomrape, by actually enfeebling or destroying the crop plants which 
are used as hosts. The weed problem is of such salient importance to 
agriculture that in many parts of the world active legislation is directed 
towards the destruction of weeds, and in this country a Seed Testing 
Station has recently been established at Cambridge to ensure the purity 
of the crop seeds sown. 
If weeds are left unchecked they will crowd out the crop entirely, and 
eventually the vegetation will revert to the natural condition for the area. 
Half an acre of wheat left unharvested in 1882 at Rothamsted was covered 
with a dense weed-flora four years later, the wheat having almost entirely 
disappeared, and now the area has reverted to woodland. The crop 
plants are usually alien and depend upon man's assistance in order to flour¬ 
ish, they are therefore unable to withstand the keen competition of the 
weeds, which are usually native or very adaptable to conditions. 
Weeds are readily distributed by the agency of wind, animals, manure, 
farm implements, etc., and in addition the seeds are often able to maintain 
their vitality for long periods when buried in the soil. Experiments have 
shown that after 32 years burial no less than three million arable weed- 
seeds can survive per acre, and after 10 years burial as many as 19 million ! 
Even after being eaten by animals and birds and voided in excreta large 
numbers of weed-seeds survive uninjured. 
Many weeds have been transferred from one part of the world to 
another, especially the commonest and most harmful weeds, which are 
very adaptable to various conditions of soil and climate. 
For some years past a weed survey has been carried out from Rotham- 
sted to determine the associations of weeds with particular soils and crops. 
A preliminary classification has been made for arable weeds, but this 
may need modification as more records become available. 
ASSOCIATION WITH SOILS. 
The nature of the soil plays an important part in determining the 
weed-flora. The first idea was that certain weeds, as individual species, 
would be characteristic of certain soils. This rarely proved to be the 
case, but instead groups of species are characteristic. There is no hard 
and fast line between the weeds occurring on different soils : with few ex- 
