262 BRITISH PLANTS 
Pasture, on the other hand, is used only for grazing 
(see p. 20). 
The continual removal of hay from the meadow tends 
to impoverish the soil, and fresh supplies of plant-food. 
must be added in the form of manure, if profitable crops 
of hay are to be obtained. The manuring of the ground 
has a big influence on the growth of all the plants, both 
grasses and weeds, but in a different way. The grasses 
grow more luxuriantly, and form such a dense shade that 
many of the weeds are killed outright, whilst others are 
so injured by the lack of light that the seed produced is 
poor in quality and small in quantity, and in time these, 
too, disappear. At the experimental station at Rotham- 
sted plots of meadow-land have received the same treat- 
ment for over fifty years, and the influence of manuring is 
strikingly shown by the relative proportion of grasses and 
weeds in the hay obtained from each plot. On un- 
manured ground less than half the hay was graminaceous 
herbage, over 39 per cent. useless weeds, and the remainder 
leguminous herbage—e.g., clover and bird’s-foot trefoil, 
which has a fairly high dietetic value. On well-manured 
ground over 99 per cent. of the hay consisted of grasses 
and less than 1 per cent. of weeds. The age of the 
meadow also is an important factor in determining the 
abundance and character of the weeds. In temporary 
meadows, laid down to grass for one year only, a large 
proportion of the weeds are annuals—relics of the previous 
year’s cultivation; but in permanent meadows they 
gradually disappear as time goes on, and in old meadows 
they are as rare as in the natural pasture. 
_ The grasses required to produce good hay must be 
quick-growing, and this can only be when an abundance 
of water is present in the soil, and the climate is warm and 
humid. Meadows are consequently chiefly found in 
valleys and on low-lying ground. On hill-slopes the con- 
ditions are unsuited to the rapid growth of the herbage, 
and the land is laid down as pasture. This artificial 
pasture forms much better grazing-ground than the 
natural pasture, for the land is specially prepared, and the 
grasses are more luxuriant and selected for the purpose 
in view. The artificial pasture is usually kept for milch- 
cows, the natural pasture for sheep. 
The most common grasses selected for laying down 
