24 IOWA STUDIES IN NATURAL HISTORY 
timber. The sow habitat in this ease will present an association 
of animals not essentially different from that of grass sod in 
general. The principal forms will be root-feeding forms of 
insect larvae, such as the white grubs and plant lice, while those 
on the surface will be caterpillars, herbaceous beetles, and plant 
bugs, accompanied by ground beetles and other predaceous 
forms. The tree-trunks provide homes and food for wood-borers, 
which with their parasites and the forms that prey upon them 
form an association. The tree-crowns with their mass of foliage 
provide for many leaf-eating insects, and thus prepare food as 
well as nesting-places for many insectivorous birds. 
Oak timber free from undergrowth. The pastured oak timber 
differs from the oak groves chiefly in factors which are incident to — 
the increased number of trees. Here we have the ground shaded 
and an increase in humidity. The ground is less thoroughly 
sodded, and strictly forest shrubs and herbaceous plants begin 
to make their appearance, when permitted to do so by the cessa- 
tion of pasturing. The annual fall of the foliage from the trees 
contributes a humus to the surface of the soil. The soi habitat 
in this ease takes on the characteristic looseness and abundance 
of decaying plant material which is typical of forest soil. This 
causes a corresponding change in the animals forming the asso- 
ciations by an increase in the number of mollusks and such 
other forms as the scavenger beetle. The undergrowth habitat is 
rarely developed to such an extent as to warrant consideration in 
a general treatise. The tree-trunk habitat and the tree-crown 
habitat differ in no essential respect from those of the oak groves. 
The forest fungus habitat becomes here established with consid- 
erable regularity. Of these fungi certain forms are commonly 
seen growing in and through the humus, while others appear 
only in or upon wood. This treatise need not differentiate be- 
tween them. Many insects, for example the fungus beetles 
(Cioidae), as well as members of perhaps a dozen other families 
of Coleoptera, feed extensively, and in many cases exclusively, 
upon fungi. In his discussion of this animal community Adams 
says:* ‘‘The general animal population of fungi is so extensive, 
including mites, sow-bugs, myriapods, and mollusks, in addition 
he oe 
