same soil.

There are also obvious cases in which different species are of service
to each other. The carpet of moss in a pine forest, for example,
protects the soil from desiccation and is thus useful to the pine; yet,
on the other hand, it profits from the shade cast by the latter.

As a rule, limited numbers of definite species are the most potent, and,
like absolute monarchs, can hold sway over the whole area; while other
species, though possibly present in far greater numbers than these, are
subordinate or even dependent on them. This is the case where
subordinate species only flourish in the shade or among the fallen
fragments of dominant species. Such is obviously the relationship
between trees and many plants growing on the ground of high forest, such
as mosses, fungi, and other saprophytes, ferns, Oxalis Acetosella, and
their associates. In this case, then, there is a commensalism in which
individuals feed at the same table but on different fare. An additional
factor steps in when species do not absorb their nutriment at the same
season of the year. Many spring plants--for instance, Galanthus nivalis,
Corydalis solida, and C. cava--have withered before the summer plants
commence properly to develop. Certain species of animals are likewise
confined to certain plant-communities. But one and the same tall plant
may, in different places or soils, have different species of lowly
plants as companions; the companion plants of high beech forests depend,
for instance, upon climate and upon the nature of the forest soil; Pinus
nigra, according to von Beck, can maintain under it in the different
parts of Europe a Pontic, a central European, or a Baltic vegetation.

There are certain points of resemblance between communities of plants
and those of human beings or animals; one of these is the competition
for food which takes place between similar individuals and causes the
weaker to be more or less suppressed. But far greater are the
distinctions. The plant-community is the lowest form; it is merely a
congregation of units, among which there is no co-operation for the
common weal, but rather a ceaseless struggle of all against all. Only in
a loose sense can we speak of certain individuals protecting others, as
for example, when the outermost and most exposed individuals of scrub
serve to shelter from the wind others, which consequently become taller
and finer; for they do not afford protection from any special motive,
su