Fig. 84.—Carl Nägeli, 1817-1891.
Von Mohl.—In 1846, eleven years after the discovery of Dujardin, the eminent botanist Hugo von Mohl (1805-1872) designated a particular part of the living contents of the vegetable cell by the term protoplasma. The viscid, jelly-like substance in plants had in the mean time come to be known under the expressive term of plant "schleim." He distinguished the firmer mucilaginous and granular constituent, found just under the cell membrane, from the watery cell-sap that occupies the interior of the cell. It was to the former part that he gave the name protoplasma. Previous to this, the botanist Nägeli had studied this living substance, and perceived that it was nitrogenous matter. This was a distinct step in advance of the vague and indefinite idea of Schleiden, who had in reality noticed protoplasm in 1838, but thought of it merely as gum. The highly accomplished investigator Nägeli (Fig. 84) made a great place for himself in botanical investigation, and his name is connected with several fundamental ideas of biology. To Von Mohl, however, belongs the credit of having brought the word protoplasm into general use. He stands in the direct line of development, while Purkinje, who first employed the word protoplasm, stands somewhat aside, but his name, nevertheless, should be connected with the establishment of the protoplasm doctrine.
Fig. 85.—Hugo von Mohl, 1805-1872.
Von Mohl (Fig. 85) was an important man in botany. Early in life he showed a great love for natural science, and as in his day medical instruction afforded the best opportunities for a man with scientific tastes, he entered upon that course of study in Tübingen at the age of eighteen. He took his degree of doctor of medicine in 1823, and spent several years in Munich. He became professor of physiology in Bern in 1832, and three years later was transferred to Tübingen as professor of botany. Here he remained to the end of his life, refusing invitations to institutions elsewhere. He never married, and, without the cares and joys of a family, led a solitary and uneventful life, devoted to botanical investigation.
Cohn.—After Von Mohl's studies on "plant schleim" there was a general movement toward the conclusion that the sarcode of the zoölogists and the protoplasm of the botanists were one and the same substance. This notion was in the minds of more than one worker, but it is perhaps to Ferdinand Cohn (1828-1898) that the credit should be given for bringing the question to a head. After a study of the remarkable movements of the active spores of one of the simplest plants (protococcus), he said that vegetable protoplasm and animal sarcode, "if not identical, must be, at any rate, in the highest degree analogous substances" (Geddes).
Cohn (Fig. 86) was for nearly forty years professor of botany in the University of Breslau, and during his long life as an investigator greatly advanced the knowledge of bacteria. His statement referred to above was made when he was twenty-two years of age, and ran too far ahead of the evidence then accumulated; it merely anticipated the coming period of the acceptance of the conclusion in its full significance.
