The cordaitean trunk was unbranched for three-fourths of the height of the tree and was topped by dense branches bearing large, simple, straplike leaves spirally arranged. The leaves had closely set parallel veins and measured from half an inch to three feet or more long. Internally, the structure of the trunks was similar to that of modern pine trunks. Casts of the pith are referred to the genus _Artisia_. The seeds were borne in clusters on branches in leaf axils. The _Cordaites_ were major contributors to some coal beds. FRUITING BODIES (Plate 5) Fossils representing many kinds of plant reproductive structures are found in Pennsylvanian rocks, but unfortunately most of them are not attached to any identifiable part of the parent plant and they cannot be assigned definitely to a particular plant. Such fossils are referred to genera and species solely on the basis of their own characteristics, although, as in other fossil classifications, such “form genera” are presumed to be parts of, or related to, the plants with which they are found in habitual association. A few such fossils, fairly common in Illinois, are illustrated on plate 5 to show their general shape and size. When attached to an identifiable leaf or leaflet, the seed is referred to as the seed of that leaf genus. For example, _Holcospermum_, a radially symmetrical seed with ribs and grooves, _Codonotheca_, a stalked, spore-bearing, lobed “cup,” and _Neuropterocarpus_, a flask-shaped seed with longitudinal ribs and grooves, all have been associated with _Neuropteris_, a leaf genus. [Illustration: Mazon Creek Strip Mine Area Showing Distribution of Spoil Heaps. The small circular areas represent waste from underground mines.] _Trigonocarpus_, commonly found as a cast of the internal part of a seed, is a trimerously symmetrical body frequently associated with _Alethopteris_. _Pachytesta_ includes preserved structures and outer layers of a seed. _Carpolithes_ is a catch-all “genus” functioning as a general term for seeds and seedlike forms whose plant group affinities cannot be determined. COLLECTING AREAS FOR PENNSYLVANIAN PLANTS Northern Illinois Plant fossils can be found in almost any northern Illinois area where Pennsylvanian rocks are exposed (see back cover), but in some places they are much better preserved and more numerous than in others. Most of the well known collecting areas and a few of the lesser known ones are discussed below. Even though some of the localities were discovered many years ago, they may indicate areas that are still favorable for collecting. Mazon Creek Area