All necessary aids to identification are included in the text itself. The identification keys make it initially possible to classify the plants according to order, family, genus, and finally, species, and the identifying characteristics of each descending class are given in detail. The morphology of each species is outlined along with data on frequency of occurrence, related soil and climate conditions, and history of past collections. An illustration showing the more important features of the species in detail is included with the decription, as well as a map indicating its geographical location in Illinois.