1862. Dr. Ed. Lucas presented the view that every fruit must be classified according to two systems:
1. Artificial; based on external characters and period of ripening.
2. Natural; based on internal characters and the fruit as a whole. In his artificial classification Lucas divides first by the season into summer, fall, and winter; each of these groups into flat, round, tapering, oblong, thus giving 12 classes. Each of these are divided into three orders according to color: '
1. Ground-colored; 2. Colored; 3. Striped.
Each of these is further subdivided into - 1. Calyx open; 2. Calyx half-open; 3. Calyx closed.
This makes a total of 228 subdivisions.
Lucas' natural system follows Diel's closely, but some of the subgroups have been raised to the rank of families, making the total 15. The first 12 are natural groups, the last 3 artificial, containing varieties difficult to classify otherwise.
Lucas' combined artificial and natural classifications give a total of 1620 separate groups. This system has had long and thorough trial in Germany, and is probably the best and most elaborate of the modern natural systems of classification. The account here given is translated from "Einleitung in das Studium der Pomologie," by Dr. Ed. Lucas, Reutlingen, Germany, 1877.