FRESH-WATER ALG.E OF THE UNITED STATES. 191 



times division has occurred ; if there be four stria% four times ; six striae, six 

 times, &c. 



Besides this method of development, in many species new cells are formed by a 

 sort of puUulation, occuring in the end cell of the filament. The primordial 

 utricle appears to rupture the wall of the distal extremity of the latter and grow 

 out into a little pullulation, or teat, which very soon becomes separated from the 

 parent cell, by the reformation, as it were, of the end wall of the latter. Tlie 

 , new little cell thus formed coats itself with cellulose, and rapidly grows, especially 

 in length, always, however, or "at least for a lengtli of time, remaining of a smaller 

 diameter than the cell from which it sprang. By a repetition of this process a 

 succession of cells is formed, each one of which, like the successive joints of the 

 field telescope, is a little smaller than its proximal neighbor and contains less 

 chlorophyl, until finally the cells are reduced to exceedingly fine, perfectly trans- 

 , parent, colorless cylinders, which together form a seta or hair. 



J lleproduction takes place among the QLdo<jontaccce, both by means of zoospores 

 1 and sexual organs. The former of these are quite peculiar, and, therefore, require 

 j especial notice. 



I Only a single one is ever produced in a cell, and there is consequently no divi- 

 ! sion of the chlorophyllous protoplasm preceding their formation. The first change 

 \ noticeable is a sort of confusion of the cell contents, the protoplasmic portion of 

 which loosens itself, as it were, from the walls, and collects in a mass at the 

 distal end of the cell. This mass after a short time assumes a more or less irregu- 

 larly globose shape, and simultaneously the parent cell begins to separate from its 

 I distal neighbor. This separation appears to take place commonly by a solution 

 I of an exceedingly fine ring of the wall of the parent-cell, just at the origin of the 

 transverse partition separating the two cells, and it is therefore brouglit about not 

 by a splitting of the end partition wall, but by a circumcision of the side walls of 

 the cell, and consequently the cavity of the latter is thrown open, tlie end wall 

 1 remaining with and closing the distal cell, whose contents have not undergone 

 f change. On the other liand, observation leads me to think that sometimes tlicre is 

 i a splitting of the end wall. According to my observation, sometimes the filament 

 is completely broken in two, but very commonly the two cells remain attached by one 

 I corner, opening from one another as it were on a hinge-joint (fig. 2/, pi. 17). 



The gathering of the protoplasm, already spoken of, into a ball, is a slow process, 

 I and the escape of this ball, through the opening formed in the manner described, 

 takes place even more slowly. The motion is not at all perceptible, with a power 

 j of a thousand or twelve hundred diameters. During the passage the ball becomes 

 more or less twisted and deformed, but as it emerges the uncompressed portion 

 sliortens and swells out, and when the mass of protoplasm is at last free in the 

 water, it soon assumes a globular or regularly ovate shape. The mother-cell, thus 

 bereft of its contents, is left dead and void. Tlic primordial utricle indeed still re- 

 mains within, but it has lost all its wonderful powers, and is nothing but a shrunken, 

 twisted, or folded dead membrane. What is the cause of tlie motion of the 

 zoospore within the cell it is very difficult to determine. It certainly is not vibrating 

 cilia. When the zoospore first escapes, it is, as already stated, an irregular lump 



