DISCOVERY OF THE CELL. 2S 



parts of plants. How growth and multiplication took place, and where exactly the 

 seat of a plant's life lay, remained, of course, obscure. It was, however, natural to 

 assume that the walls of these small cells constituted the essential part and living 

 substance of plants, that they drew materials from the fluids which rose by suction 

 in the tubes, and so increased in size and were renewed. 



It was as yet hardly suspected that the slimy substance which filled the cells. 

 of a plant, like honey in a honey-comb, was the basis of life. The observation made 

 again and again at the beginning of the nineteenth century, that the cell-contents- 

 of certain algse are extruded in the form of globules of jelly, and that each globule 

 moves independently and swims about in the water for a time, but then comes to- 

 rest and becomes the starting-point of a new alga, might undoubtedly have led 

 to this conclusion. The accounts of these occurrences were, however, considered 

 incredible by the majority of contemporary observers; and it was not till recently, 

 when Unger established the phenomenon as an indubitable fact, that a proper 

 estimation of its value was accorded. In the year 1826 this botanist investigated 

 under the microscope a water-weed found at Ottakrinn, near Vienna, which had 

 been described by systematic writers as an &.lga, and named Vaucheria clavata. 

 To the naked eye it appears like a dense plexus of dark-green irregularly branched 

 and matted filaments. These filaments, when magnified, are seen to be tubular cells- 

 which wither and die away at the base whilst growing at the apex, and developing 

 sac-like branches laterally. (Fig. 25a.) The free ends of these tubes are blunt and 

 rounded. The substance they contain is slimy, and, though itself colourless, is 

 studded throughout with green granules; whilst near the blunt end of each filament 

 these green particles are so closely packed that the entire contents of that part 

 appear of a dark-green colour. 



Now, there comes a time in the life of every one of these filaments when its- 

 extremity swells and becomes more or less club-shaped. The moment this occurs 

 the dark-green contents withdraw somewhat from the extremity, leaving it hyalina 

 and transparent. Almost simultaneously the contents of the swollen part of the 

 tube nearest the apex become transparent, whilst further down the colour becomes 

 very dark. (Figure 25a, a.) Twelve hours after the commencement of this change, 

 that portion of the tube's contents which occupies the club-shaped end separates 

 itself entirely from the rest. A little later, the cell- wall at the apex of the tube 

 suddenly splits, the edges of the slit fold back, and the inclosed mass travels 

 through the aperture (fig. c). This jelly-like ball, having a greater diameter than 

 the hole, is at first strangulated as it struggles forward, so that it assumes the shape 

 of an hour-glass and looks for an instant as if it would remain stuck fast. There 

 now arises, however, in the entire mass of green jelly an abrupt movement of 

 rotation combined with forward straining, and in another instant it has escaped 

 through the narrow aperture and is swimming freely about in the surrounding 

 water (fig. d). The entire phenomenon of the escape of these bodies takes place- 

 between 8 and 9 A.M., and, in any one case, in less than two minutes. When free, 

 each individual assumes the shape of a perfectly regular ellipsoid (fig. d), having 



