39 Dr. F. Cohn on the Development and Propagation 



remarkable ; one might imagine sometimes that they had settled 

 quite to rest, but after an interval of an hour or more they sud- 

 denly recommence their old revolutions. 



At the time when the swarming-cell breaks through the mem- 

 brane of the spore of Sphcey^oplea, it possesses no cellular mem- 

 brane; but it produces this while still in- motion, so that it 

 becomes distinctly surrounded by a delicate, young, and very 

 elastic cellulose coat. When the swarming-cell germinates, this 

 membrane becomes rigid and prolonged at both ends so as to 

 produce the spindle-shape; these ends grow out rapidly into 

 capillary points, which constantly increase in length ; the middle 

 of the germinating cell then likewise extends itself, the ends 

 being pushed still further apart, and the entire cell is thus ren- 

 dered at once longer and thicker. The originally homogeneous, 

 finely-granular contents of the swarming-cell is changed in ger- 

 mination, the remainder of the red oil becoming rapidly con- 

 verted into chlorophyll, the germinating plant thus acquiring a 

 uniform green colour ; but even in the earliest condition colour- 

 less bubbles {vacuoles) are found in the green plasma, these 

 vacuoles containing a fluid of less density, while the chlorophyll 

 between them is compressed, and thus assumes the form of green 

 rings standing at certain distances apart. In these streaks 

 large starch-globules are soon secreted, and by the time the 

 germinating plant is j^ of a line long, it has already assumed 

 the full character of the cells of Sphceroplea. It continues to 

 increase in length and breadth, retaining however its Closterium- 

 like shape. I met with colossal spindle-shaped cells half a line 

 and more long, prolonged into capillary points at both ends. 

 Sphceroplea is the only Conferva known to me that never pos- 

 sesses a root; in all other genera one end of the germinating 

 filament, avoiding the light, grows downward into an organ of 

 attachment, while the other differently formed end grows by 

 apical development into the proper filament. In Sphceroplea, 

 not only are both extremities of exactly the same shape from the 

 first origin, but no apicular growth occurs, at least not after the 

 capillary ends are completed; the cells here grow in the middle. 

 Since the green rings in the cells of SpJiceroplea fix the relative 

 positions of their points, the places where the growth takes place 

 may be readily observed, the number of rings being constantly 

 multiplied, by the division of the old, previously formed ones. But 

 a minute investigation of this subject would carry us too far from 

 the object of this notice. After some time the germ-cell divides 

 in the middle, and with the enlargement of the plant the number 

 of cells is increased : the length of the cells is strikingly unequal, 

 for while in some cells they cannot be perceived, other cells are 

 only \ or ^^ of a line. But in the longest, many-celled filaments, 



