IV. On the continuity of the protoplasm through the walls of vegetable cells

Abstract

Since the communications of November 11th, 1882, and April 16th, 1883, the author has been chiefly employed in testing and improving; his methods, and adding to the number of plants in which he has been able to demonstrate the existence of a continuity of the protoplasm between adjacent cells. In certain endosperm cells, e. g ., Bentinckia Conda-panna, where the protoplasmic thr eads traversing the cell walls are particularly well developed, it is possible to see the threads perfectly clearly by merely cutting sections of the endosperm, and mounting them in dilute glycerine. Taking the structure displayed by such a preparation as normal, the author has compared it with the preparations obtained after the action of Chlor. Zinc. Iod. and sulphuric acid. He finds that his method of swelling with Chlor. Zinc. Iod., and staining with Picric-Hoffmann Blue, is in every way perfectly satisfactory, since but little alteration of the structure occurs, and the staining with the Picric-Hoffmann Blue is limited to protoplasm. The sulphuric acid method is in the main unsatisfactory, although it is valuable in the case of thin-walled tissue, where violent swelling must be resorted t o ; and it is also valuable as affording most conclusive evidence of the existence of a protoplasmic continuity in those cases where the protoplasmic processes of pits cling to the pit-closing membrane. He believes, however, that the results obtained Can only be rightly interpreted in the light of the results obtained with Chlor. Zinc. lod. The possibility of seeing the threads depends upon their degree of tenuity and upon the thickness of the pitclosing membrane, and in extreme cases and in w hat are by far the more general cases, the only evidence of such perforating threads is afforded by the general staining of the pit-closing membrane. Every transition between clearly defined threads in the substance of the closing membrane and the mere staining of that structure as a whole occurs. The author has found that in all pitted tissue a pit-closing membrane, which is made evident by staining thin sections with iodine and mounting in Chlor. Zinc. Tod., is uniformly present, and th at open pits do not occur. The continuity of the protoplasm is always established by means of fine threads arranged in a sieve-structure, and not by means of comparatively large processes which the occurrence of open pits would necessitate. He cannot therefore agree with observers whose statements necessitate the existence of such open pits.