Publisher's Synopsis
Excerpt from Journal of the Royal Microscopical Society, Vol. 4: Containing Its Transactions and Proceedings, and a Summary of Current Researchers Relating to Zoology and Botany (Prinicipally Invertebrata and Cryptogamia), Microscopy, &C.; Part I
To understand clearly the structure of the growing point, it is necessary to examine Specimens from which the cell-walls have been. Removed: this can be accomplished by soaking for several hours in a solution of nitro-pierio acid. If this material is stained and examined under a high power, it will be seen that the proto plasm of each cell is in perfect continuity with the next above and below, being connected by a narrow neck of protoplasm. In addition to this central string, which is comparatively thick and strong, much finer threads may sometimes be seen springing from one of the masses of protoplasm just within its margin, and joining on to the next mass in the same position.
These marginal strings were for some time a source of much perplexity, as owing to their extreme tenuity they rarely survived, unbroken, the treatment necessary for the removal of the cell-walls, and, if broken, the protoplasm contracts so much, that not a trace of the torn ends remain. (pl. VI. Fig.
If a small amount of pressure, combined with a rotatory move ment, be applied to the thin glass cover protecting the specimen under examination, the segments of some of the growing points will be separated from each other. Examined in detail, these segments in Polysiphonia 1110601011511 present the following appearance. The first below the apical cell resembles a thin Circular disk with an unbroken margin; the second working backwards from the apex is slightly thicker than the preceding, and the margin has four notches at equal distances; these notches, in the third segment, reach about half-way from the centre to the circumference of the disk, which thus presents the appearance of a Maltese cross; in the segments further back, the four lobes are more or less quadrate in form, and each is joined to the central mass of the segment by a narrow neck of protoplasm (fig. The central mass of the segment developes into the axial cell of one joint of the stem, and the four outgrowths form the four cortical cells. The slender threads, alluded to as springing from near the margin of the disk, are in P. Ureeolata four in number, and unite the superposed cortical cells of adjoining segments. The cortical cells are thus connected with each other by vertical protoplasmic threads, each one again communicating with the axial cell by a horizontal thread, while the axial cells, as already shown, are connected by vertical threads (fig. This mode of formation of the cortical cells, as also their connection with each other and with the axial cell, is the same in all the species of Polysiphonia that I have had an opportunity of examining.
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