Since these rules are applicable only in beech forests, much mischief and misconception resulted from their generalization; pure, even-aged high forests became the ideal, and the mixed forest, which was originally the most widespread condition, vanished to a large extent. This was especially unfortunate in Northern and Northeastern pine forests. A reaction against Hartig’s generalization began about 1830, under the lead of Pfeil. He had at first agreed with Hartig, and then with equal narrowness advocated for many years a clear cutting system with artificial reforestation. Finally, however, he was not afraid to acknowledge that his early generalizations in this respect were a mistake, and that different conditions required different treatment. In the development of the shelterwood system there was at first, under the lead of Hartig, a tendency to open up rather sharply, taking out about three-fourths of the existing stand, but gradually he became convinced that this was too much, and finally reduced the first removal to only about one-third of the stand. This was the origin of his nickname of _Dunkelman_. In spite of the fact that it was claimed that Cotta took the opposite view (for which he was called _Lichtman_), he, too, grew to favor a dark position, and, as he progressed, leaned more and more towards more careful opening up. Hartig originally recognized only three different fellings: the cutting for seed; the cutting for light; and the removal cutting. By and by, a second cut was made during the seed year, and the number of fellings to secure gradual removal were increased, so that, by 1801, this system seems to have been pretty nearly perfected to its modern conditions. The best exposition of this _Femelschlagbetrieb_ (shelterwood system), as then developed, is to be found in Karl Heyer’s Handbook, 1854. The method was unfortunately extended by Burgsdorf (1787) to the Northern pineries with a seventy year period of rotation. Within ten years, however, he recognized its inappropriateness, and modified it by instructions to leave only six to twelve seed trees per acre. His successor, Kropff, reduced the number of seed trees to four or five, which were to be removed within two or three years. In spite of the development of this more rational method, the practitioners under Hartig’s approval, held mainly to a dark position even for pine, much in the manner of a selection forest, which produced a poor growth of oppressed seedlings, retarding for a long time the development of the pineries.