FRESn-WATER A L G .E OF THE UNITED STATES. 103 



the cell, along the outer zone, and granules can be always seen passing backwards 

 and forwards with an unsteady motion. 



When the streams of protoplasm are setting very actively from the centre to- 

 wards one end, there will often be an accumulation of the protoplasm there, and a 

 consequent decided lessening in the size of the vacuole, which Avill again expand 

 as the return currents arouse themselves. Within the vacuoles are seen more 

 or less numerous smaller or larger granules in active busy motion, swarming over 

 and about one another with an unsteady hurrying to and fro. 



A form of motion, similar in appearance to this, but probably of different signi- 

 ficance, is seen in most desmids when in an unhealthy feeble condition. I 

 have seen it most marked in Cosviarium margaritaceum. In such fronds the endo- 

 chrome has lost its deep green color, and become shrunken, and lying within it is 

 a great space containing myriads of minute blackish particles swarming about 

 actively. This peculiar state and appearance is by no means confined to the 

 desmids, for I have seen it very highly developed both in species of Spirogijra and 

 (Edogonium. It appears to be connected with decay. Is it possible tliat these 

 minute particles are foreign to the plant, vibrionic in nature] 



In regard to the nature of the movements seen within a healthy desmid, some 

 have viewed them as exceedingly mysterious, the result of the presence of 

 cilia, &c. ; but these views have been so thoroughly exploded that it is scarcely 

 necessary even to mention them here. The movements are, in truth, precisely 

 parallel to the so-called cyclosis of the higher plants. Protoplasmic germinal mat- 

 ter, wherever it exists, be it in animal or vegetable, has as one of its distinguish- 

 ing characters the power of active, spontaneous, apparently causeless movements, 

 and it is simply the carrying out of this power or attribute which has attracted so 

 much attention in the desmids, because it is in them so readily seen. 



There are, in this family, two distinct methods in which the species are multiplied 

 one with, the other without, the intervention of anything like sexuality. The 

 non-sexual method of increase is really a modification of an ordinary vegetative 

 process, a peculiar cell multiplication by division. In such fronds as tliose of the 

 genus Cosmarium, which are composed of two evident halves connected by a 

 longer or shorter isthmus, the first step in the process is an elongation of this neck. 

 In a very short time there appears around the centre of this a constriction, and I 

 believe an actual rupture of the outer coat. By this time a new wall has formed 

 inside each Jialf of the isthmus, and stretches also across its cavity, forming witli 

 its fellow a double partition wall, separating the two halves of the old frond. 

 Rapid growth of the newly formed parts now takes place, the central ends become 

 more and more bulging as they enlarge, and in a little time two miniature lobules 

 have shaped themselves at the position of the old isthmus. These are at first 

 small, colorless, and destitute of all markings, looking, as Mr. Ealfs says, like con- 

 densed gelatine. They, however, rapidly increase in size and firmness, their con- 

 tents assuming a green color and their walls taking on the peculiar markings of 

 the species. At last, the parts thus formed having assumed the shape and appear- 

 ance of the original lobules, the two fronds, which have been developed out of one, 

 separate, mostly before the new semicells have acquired their full size. 



