160 FRESH-WATER ALG^E OF THE UNITED STATES. 



composed of a varying number of cells placed, end to end, all alike, and each of 

 them apparently independent of its associates. Each cell in one sense is, therefore, 

 a perfect, complete individual, capable of living dissociated from its companions. 

 How far the life of one of these cells is influenced by that of its neighbors is un- 

 certain, probably to a slight extent, possibly not at all. At any rate, they are so 

 far independent that the filament is rather a composite body than a unit of life. 

 These cells are cylindrical, with the ordinary cellulose wall, which can commonly 

 be stained blue by iodine and sulphuric acid, and is often distinctly composed of 

 layers, but never has any " secondary markings," each layer being precisely like 

 that superimposed upon it. Outside of the wall is a jelly-like sheath, which is 

 mostly not discernible from its thinness and transparency, although it no doubt 

 exists, as is proven by the slipperiness of the general mass. The primordial utricle 

 is always present. The chlorophyl is variously arranged, most generally in bands, 

 either straight or spiral, sometimes in definite irregular masses, sometimes diffused 

 through the cell. Imbedded in it are, at certain seasons, numerous minute, gene- 

 rajly shining, granules, which are either minute specks of starch, or little drops of 

 oil. Besides these there are contained in it, especially in the bands of chlorophyl, 

 more or less numerous comparatively large, oval or roundish bodies, with a distinct 

 outline and a deeper color than the surrounding portions. These masses are pro- 

 toplasm, dyed with chlorophyl-green, and are believed to be especially active in 

 the formation of starch. At times, iodine turns them simply brown ; at others it 

 colors their inner portions blue and their outer brown, showing them to contain 

 starch. The general cavity of the cell is occupied by fluid, in which is placed the 

 nucleus. This is mostly single, but rarely, according to Naegeli and other authori- 

 ties, double, and De Bary states that he has seen three nuclei in a single cell. I 

 have "never seen more than one, and think that even this is not rarely absent, having 

 certainly repeatedly failed to demonstrate its presence. It is colorless, often with 

 a nucleolus, transparently bright, irregular in form, placed in the centre of the cell 

 with numerous arms radiating out from it, some of them ending within the cell, 

 others connecting it with the primordial utricle. De Bary states that this nucleus 

 occasionally is tinged green with chlorophyl, I do not remember ever to have seen 

 it so. 



I have not infrequently seen numerous minute dark granules, similar to those 

 seen in Closterium, scattered through the inside of the cell, in active motion. Some- 

 times they are to be found collected in vast numbers near the ends of the cells, 

 dancing and swarming about one another, and passing off in small streams from 

 one end to the other, coasting along close to the primordial utricle, in a word, ex- 

 hibiting precisely the same motions as are so common among the desmids. 



The Zygnema filament grows in length by a process of cell multiplication by 

 division of the simplest kind. It seems to be somewhat uncertain whether the 

 nucleus always divides into two as a part of the process or not. These plants 

 multiply both by the separation of cells and their subsequent growth, and, by 

 means of resting spores, the so-called Zygospores. 



The first appearance of separation of the cells is an evident disposition to the 

 rounding off of the ends of the cells. The corners are first rounded and separated 



