ON THE MIXED HERBAGE OF PERMANENT MEADOW. 
1213 
with particular manures, then it is found that just as certain orders, taken collec¬ 
tively, say grasses, and Leguminosse, have opposite tendencies and different require¬ 
ments, so certain species of the same Order and even of the same genus may exhibit 
contrary phenomena. Just as Leguminosse as a whole may be practically banished, 
and Graminese made to prevail, so certain species of Graminese or of Leguminosse can 
be driven out, or, at least, some particular species may be so greatly favoured that the 
others are banished, either by the superior vigour exhibited by the victorious species, 
or by the directly injurious agency of the manure applied. From this point of view 
the comparative details hereafter given as to various members of the same genus which 
exhibit opposite tendencies, especially Poa pratensis and Poa trivialis , and the different 
species of Arena , which nevertheless manifest very opposite tendencies, may profitably 
be studied. 
This opposite tendency between nearly allied plants (further illustrated by the 
occasional impossibility of grafting, or of mutually fertilising, allied species), is a most 
interesting phenomenon, and of great importance from both a scientific and a practical 
point of view. Several illustrations of it will appear further on ; meanwhile we may, 
in passing, allude to the necessity for caution in the interpretation of isolated experi¬ 
ments which this fact demonstrates. Because a particular grass, or other plant, is 
little benefited by ammonia-salts, for instance, it does not follow that it will not be 
favoured by nitrates ; nor, because if while growing in association with other species it 
may not be specially benefited by a particular manure, does it follow that it would not 
derive advantage from the same substance when growing separately. 
The alleged antagonism of certain plants has been supposed to be due to the 
injurious effects of root-excretions ;' 7r but this supposition is, to say the least, not 
a sufficient explanation of the observed phenomena. The true explanation of the facts 
recorded lies probably in the varying conformation and requirements of different 
plants, as will be illustrated in subsequent sections. The advantages derived from 
the practice of rotation also receive illustration from these same circumstances. 
Habit and Conformation of Plants : Organisation by means of which they maintain 
or improve their position, or succumb in competition with others. 
Before passing to the consideration of individual species, a few general remarks on 
the structure and mode of life of the plants with which we have to deal are requisite. 
All the plants are, indeed, well known, and many of the facts we have to call 
attention to are equally familiar. Nevertheless, it is important to note the points of 
greatest significance in the consideration of the endowments by virtue of which plants 
growing in association maintain their position, prevail over, or succumb to their 
competitors. 
* See A. P. De Candolle, ‘Physiologic Yegetale,’ p. 1474; Duchaetre’s ‘Elements de Botanique,’ 
p. 246; Braconnot, ‘Ann. Phys. et Clymie,’ 1839, t. 72, p. 27. 
MDCCCLXXXII. 7 q 
