AGREEMENT OF COMMUNITIES ; 307 
Some investigators have questioned the importance of vegetation 
to animals and we note here that the distributions of plant and animal 
species are not always correlated. If one refers to species of plants 
and species of animals then the vegetation very often is not correlated 
with the distribution of the animals. If on the other hand one means 
that the plants are controllers of physical conditions, then vegetation 
can be said to be of very great importance. 
Before discussing the problem of agreement between plant and 
animal communities, it is necessary to state what is meant by agreement. 
According to present developments of the science of ecology plant and 
animal communities may be said to be in full agreement when the growth 
form of each stratum of the plant community is correlated unth the conditions 
selected by the animals of that stratum. Questions of agreement are pri- 
marily questions for experimental solution. Two types of disagreement 
are to be expected. We may illustrate the first by a bog or marsh 
community. Considering plants rooted in the soil we note that water 
is secured from the soil by the roots and is lost through the leaves and 
twigs. Accordingly since bog soil is unfavorable, due to the presence 
of toxins or to other causes, plants growing in it do not secure water 
easily even when the quantity of soil water is great. Such plants have 
xerophytic structures (which tend to check the loss of water) developed far 
beyond the requirements of the atmospheric conditions surrounding their 
vegetative parts. It is improbable that the animals inhabiting a bog- 
vegetation field stratum would select atmospheric conditions such as 
produce equally xerophytic structures under favorable soil conditions. 
We may therefore expect disagreement. The smaller plants such as 
fungi, algae, etc., are related to the strata of soil and atmosphere exactly 
as the smaller animals and as much disagreement is to be expected between 
such plants and the rooted vegetation as between the rooted vegetation 
and animals. It must also be noted that the xerophytic structures of 
the plants of unfavorable soils may have important influence upon ecto- 
phytic plants and animals and in part counteract the effect of favorable 
atmospheric conditions. 
The second type of disagreement is represented by cases in which 
the vegetation lags behind. We have already noted that on the clay 
bluff pp. 209-(17) conditions become favorable for inconspicuous plants 
and forest animals as soon as the growth of the pioneer vegetation gives 
shade to the soil. In other cases woody vegetation remains in situations 
where the conditions have become unfavorable for it and the less con- 
spicuous plants and some of the animals have disappeared. We may 
