94 PLANT LIFE ON THE FARM. 
The grasses, both in number of species and in relative 
and actual amount of produce, exceed the plants of all 
other orders. The lowest produce occurs on the con- 
tinuously unmanured plots; the highest on those to 
which a highly nitrogenous manure, such as ammonia 
salts or nitrate of soda, is continuously applied in combi- 
nation with earthy and alkaline salts—especially potash. 
But while the total gramineous produce is thus increased. 
by the description of manure just mentioned, the num- 
ber of species of grass is reduced. On the unmanured 
plots, on the average, sixteen different sorts of grasses 
may be found, each contributing a fair proportion to the 
total herbage ; thirteen only are found on the highly 
ammoniated plots, and of these only a very few contribute 
materially to the crop, the remainder being present in 
such small quantities as to make but little difference in 
the totals. 
The principal external characteristics which favor the 
growth of the grasses in their competition with other 
plants are their dense root-growth, monopolizing as it 
were all the soil within reach, and affording little power 
to the roots of other plants to penetrate the mass. To 
an extent variable in different species, this root-growth 
is both superficial as well as deep.. In addition to this 
generally amplg root development, many of the species 
are aided in the struggle by their stout tufted habit and 
specially by their power of producing creeping offshoots 
above or below ground which insinuate themselves in 
between other plants and occupy any vacant territory. 
No doubt internal anatomical differences are even of 
greater moment than these external characteristics, but 
these demand minute comparative study by means of the 
microscope, under various conditions, and at different 
seasons, and constitute a branch of inquiry at present 
hardly even entered upon. 
Although grasses as a whole comport themselves in a 
