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MESSRS. J. B. LAWES, J. H. GILBERT, AND M. T. MASTERS, 
small proportion and amount. The “ predominance/’ like the “ absence,” is determined 
by observation during growth each season, as well as by the less frequent botanical 
analyses of samples of the produce. By such observations and analyses a much more 
correct estimate of the actual degree of preponderance of individuals of particular species 
in a given area is gained than is indicated by the usual terms of “ common,” “ rather 
common,” “ rare,” “ very rare,” and the like, which give but a very imperfect idea of 
actual or relative predominance.* Moreover, the species predominant in one season 
are not necessarily so in another. We have, therefore, a means of studying the special 
influence of climate, of manures, or of the innate characters of the plant itself, which is 
of great value in the consideration of the struggle for existence among plants. If, for 
instance, in the same season a species is dominant on a grea,t number of differently 
manured plots, it may be inferred that its dominance is due not directly to the agency 
of a particular manure, or to the climatal conditions alone, which were common to all 
the plots, but largely to the habit of the plant itself. The predominance of Festuca 
ovinct, for instance, already referred to, and its tendency to spread, as shown by the 
circumstance that it was dominant in the first year of separation on two plots, in the 
second on eight, and in the third and fourth on thirteen, are obviously due rather to a 
superior power of endurance in the plant itself compared with its competitors, than to 
directly favourable conditions of manuring or of season. On the other hand, some 
species are dominant on some plots, but are absent from, or exist only in small propor¬ 
tions on others. In such cases it may be assumed that the particular manure has been 
either directly favourable or prejudicial to the plant, or indirectly so by favouring or 
discouraging the growth of others. Again, if a species be dominant on a particular 
plot, or on a group of plots more or less similarly manured, the inference is that the 
manure is directly beneficial to the plant. 
The Grasses. 
Passing to the consideration of the particular plants met with on the various 
experimental plots, first in order come the grasses, which constitute the most numerous 
and most important of their occupants. 
Before describing the individual gramineous species occurring on the plots, it will 
be well to make a few general observations on them collectively. 
The species which occur in the experimental field are, almost without exception, 
perennials, and they have generally a tufted habit of growth, especially under the 
influence of suitable manures. They have all more or less branched fibrous roots, 
consisting of a multitude of fine threads, which descend to various depths, and whose 
degree and manner of ramification vary according to the species, and to the conditions 
of manuring, association, and season. They never form a thick tap root, as some of 
the Leguminosse and many of the miscellaneous plants do. Nor have they much 
* See Alph. de Candolle, ‘ Geog. Bot.,’ vol. ii., p. 1154. 
