Page:Microscopicial researchers - Theodor Schwann - English Translation - 1947.pdf/282

248 CONTRIBUTIONS TO If we now assume a cell to be completely filled with a transparent solution of sugar in which there is rapidly generated just so much gum, as may form, by an equally quick conversion into jelly, a delicate cell-membrane, the existence of which we cannot possibly recognise with the microscope, in consequence of the similar refracting power of the wall, the contents, and the surrounding medium; it then becomes exceedingly probable that a number of such formative processes may go on which escape our observation, and become known to us only in their results, when, after the absorption of the parent-cell, we suddenly find two new ones in its place. If, on the other hand, our attention has been previously directed to this process, we have, in the application of reagents, especially iodine, which is quite indispensable to the physiological botanist, several means of rendering it visible in instances where it is suspected to be going forward. Gradual transition to the completely invisible processes are readily found by more extended investigation; I will just mention one of the most difficult instances which I have met with, by way of example. It occurs in the germination of the sporules of Marchantia polymorpha. Only a few, generally only from two to four of the cell-nuclei which appear in the sporules, serve for the formation of cells; the others become quickly enveloped with chlorophyll, and are thus withdrawn from the vital process. The transparent fluid, however, in which these cytoblasts float, passes through the remaining stages of the metamorphosis into cell-membrane only just at the boundary of the latter, and with such rapidity that the exceedingly delicate young cells cannot be distinguished by anything else than a minute, generally more or less uninterrupted circle of infinitely small, black granules, and by a scarcely perceptible greater transparency of the contents of the newly-formed cells in comparison with that of the parent-cell, and finally, under the most favorable circumstances, by the spot at which the newly-developed cells come into contact, the point of juncture being still covered by the membrane of the parent-cell. (Pl. I, figs. 18-20.) This may perhaps be general in the Cryptogamia, and especially in water plants, and probably Mohl’s division of the cells of Confervæ may be thus explained.

If we consider, however, that there are undoubtedly many plants, among which the Fungi and infusorial Algae should pro-