Page:Microscopicial researchers - Theodor Schwann - English Translation - 1947.pdf/27



ALTHOUGH plants present so great a variety of external form, yet they are no less remarkable for the simplicity of their internal structure. This extraordinary diversity in figure is produced solely by different modes of junction of simple elementary structures, which, though they present various modifications, are yet throughout essentially the same, namely, cells. The entire class of the Cellular plants consists only of cells; many of them are formed solely of homogeneous cells strung together, some of even a single cell. In like manner, the Vascular plants, in their earliest condition, consist merely of simple cells; and the pollen-granule, which, according to Schleiden’s discovery, is the basis of the new plant, is in its essential parts only a cell. In perfectly-developed vascular plants the structure is more complex, so that not long since, their elementary tissues were distinguished as cellular and fibrous tissue, and vessels or spiral-tubes. Researches on the structure, and particularly on the development of these tissues, have, however, shown that these fibres and spiral-tubes are but elongated cells, and the spiral-fibres only spiral-shaped depositions upon the internal surface of the cells. Thus the vascular plants consist likewise of cells, some of which only have advanced to a higher degree of development. The lactiferous vessels are the only structure not as yet reduced to cells; but further observations are required with respect to their development. According to Unger (Aphorismen zur Anatomie und Physiol. der Pflanzen,