low (1814) is incorporated matter borrowed from the results of his researches.
It thus appears that the field of the present Atlantic Middle States had been explored with considerable energy before Muhlenberg's time. New species of plants had been discovered and additional information had been gained concerning species already known. The scientific value of these observations, attested by the herbariums which still exist, and by what Muhlenberg furnished for publication, is enhanced and interest is added to them by a careful perusal of Muhlenberg's correspondence, a part of which he kept and is now preserved by the Historical Society of Pennsylvania. These letters—some from European naturalists and others from American—were written in the last sixteen years of the eighteenth century and the first and part of the second decades of the nineteenth, and are often annotated with Muhlenberg's remarks. Of his own letters only a few copies are present, chiefly those which he wrote between 1791 and 1794 to Dr. Manasseh Cutler, of Ipswich, Mass. Further, a number of letters from various students and note-books, botanical notices, descriptions, and outlines in Muhlenberg's handwriting are in the possession of his descendants, or have been handed over by them to scientific societies.
The note-books bear witness to the earnestness with which Muhlenberg took up and pursued his botanical studies after his flight from Philadelphia. During the year 1778 may be found numerous descriptions of plants like that of Eupatorium purpureum, trumpetseed or gravel root; to which are added such notes as "is probably Eupatorium (altissimum)." Doubtful remarks of the kind abound. "Is it probably Actea?" "It may be Azalea?" "Perhaps it is Convallaria?" It is evident from such notes that Muhlenberg had not advanced far in acquaintance with the wild plants in the summer of 1778. In the same year he seems to have drawn up a plan of studies by the systematic execution of which he could hardly fail to acquire the desired knowledge. Its most notable points are as follows: "How may I best advance myself in the knowledge of plants? It is winter, and there is little to do. In winter I must select such plants as I can easily remove. . . . Toward spring I should go out and form a chronology of the trees, how they come out, and of the flowers, how they appear, one after another. . . . I should especially remark the flowers and fruit; and there are many other circumstances, but none quite so essential.
"1. The flower, the time, the part of the plant it stands on, whether there are stamens, and how many; the pollen; whether there are pistils, and how many; their shape; whether and how there is a corolla; its color and shape; whether and how there is a calyx.
