52 FARM GRASSES OF THE UNITED STATES 
On the Pacific Coast a species of fern (Preris aguz- 
lina) is the worst weed in grass-lands, particularly 
west of the Cascade Mountains, in Washington and 
Oregon. It is provided with rather formidable under- 
ground stems, and is difficult to eradicate. It may be 
held in check by cutting twice or three times a season. 
When young and tender, sheep and goats will eat it, 
and it may be eradicated by stocking the land heavily 
with these animals. It does not bother much on land 
that is plowed eight or ten inches deep once a year, 
and hence is not very troublesome on well-cultivated 
fields. 
MANURING GRASS-LANDS 
The use of fertilizers is one of the most unsatisfac- 
tory subjects to handle in the whole range of agricul- 
tural science. It is now just one hundred years since 
the first carefully planned fertilizer experiments were 
laid out by a modern investigator. Sixty-two years 
ago Liebig’s great work was published, in which the 
theory was announced that by analyzing the soil and 
the crop the chemist could prescribe the fertilizers to 
be applied in any given case. ‘This theory was the 
basis of the work of the agricultural chemists for half 
a century. Innumerable fertilizer experiments have 
been conducted with the utmost care. The soil has 
been analyzed times almost without number. The 
constitution of the mineral matter removed from the 
soil by plants has been determined to a nicety. It is 
definitely known that chemical fertilizers frequently, 
we may say usually, exert a decidedly favorable influ- 
ence on growing crops. It is absolutely impossible, 
however, to say just what fertilizers or how much of 
