At some point in the key there will be found for each plant a statement in parentheses. This is general information concerning the height of the plant, the color of the flowers, or the season of bloom. It must be remembered that the height of plants is subject to great variation; that most plants have white-flowered varieties; and that the month of bloom depends largely on the latitude and the climate. Therefore this general information should not be used as means of distinguishing species. =The names of plants.= Each plant bears a scientific name. This is composed of two parts and is usually of Latin or Greek derivation. In some cases these names are taken directly from the Latin language, as _Quercus_, the Oak, or _Acer_, the Maple. In other cases the name may indicate some characteristic feature of the plant, as _Polygonum_, many joints, for the Knotweed, or _Ammophila_, sand-loving, for the Beach Grass. An English name is also given for almost every kind of plant. In a few cases there is no accepted English name, and none has been given. In many cases the same English name applies to several kinds of plants and has been repeated for each. When this is so, the common name is given in the key in parentheses before the scientific name is reached. Thus, if one is satisfied to know merely that his plant is a dandelion, he learns it in line 17b of the key to the Composite Family, but to discover which kind of a dandelion he has, he must follow through the key and use the scientific name. There is in this book, therefore, no necessity of learning or using scientific names. The less critical may be satisfied with an English name, and others may use the scientific names as they see fit. =Possible Errors.= In using this book, care must be taken to compare all the lines under each number with the plant, and to use judgment in selecting the right one. While faulty observation or poor judgment may lead to error, a mistake is usually due to carelessness in not following correctly the reference at the end of the line chosen. If one reaches a number in which none of the lines of description agrees with the plant, it is very probable that he has made a mistake at an earlier stage of the identification, and he should then begin anew. It has been the intention of the author to make the key as nearly as possible proof against errors of judgment. For example, the Indian Turnip may be sought under either Group 3 or Group 4; the Matrimony Vine may be identified either as a shrub or as an herb, and numerous other similar examples may be discovered. =Botanical Information Needed.= It is presumed that those using the book will be familiar with the parts of the flower and with the commoner descriptive terms applied to leaves. Unusual terms have been avoided as far as possible, but those which do occur, as well as the simpler ones, are explained in the glossary.