Page:History of botany (Sachs; Garnsey).djvu/355

] the wall without the cell. Since the contents are the essential part of the cell and form a separate and individual whole which has its own membrane-like boundary, the primordial utricle, before the secretion of the membrane of cellulose, we must either confine the term cell to the enveloping membrane or to the chamber which it forms and find another name for the body of the contents, or else call this the true and proper cell. This, which presents itself at once as the correct mode of conception to anyone who observes the formation of swarm-spores in Algae and Fungi and many other cases of cell-formation, was from this time forward a vital point in the doctrine of the cell. Braun contributed also to the clearing up of the ideas of botanists on this subject by bringing together under one systematic view and classifying all the varieties of cell-formation which were known to him up to the year 1850, and especially by a more searching investigation into modes of conjugation. Henfrey's contributions ('Flora' of 1846 and 1847) rested entirely on the observations of German botanists, and brought to light nothing that was independently and essentially new. On the other hand Hofmeister's new observations on the development of pollen (1848), and his many remarks on cell-formation in his epoch-making researches into embryology in 1851, contributed repeatedly to the deciding of doubtful points, especially in the behaviour of the nucleus in cell-formation and the production of the dividing walls. Von Mohl, who in spite of his own excellent observations maintained up to 1846 a somewhat undecided attitude of mind in respect to Schleiden's theory, which was at that time still in vogue, published in 1851, in his treatise 'Die vegetabilische Zelle,' an excellent summary of the results which had been so far achieved. In describing cell-division he notices specially that the new nuclei occupy the centres of the future daughter-cells before the division of the contents commences; but he still clung to his old view, that in every instance of