li)2 FRESH-WATER ALG^ OF THE UNITED STATES. 



of strongly clilorophyllous protoplasm, homogeneous or with one or more roundish 

 masses of darker green within it. As it assumes its shape, however, a very dis- 

 tinct transparent spot appears at its smaller end. Whether this is an absolute 

 vacuole or not, I have never been able to satisfy myself, but I am rather inclined 

 to believe that it contains highly refractive transparent protoplasm. As this spot 

 is perfected the cilia make their appearance. Whether they are actually first 

 formed there, or whether, as is more probable, they are formed inside the cell, and 

 are so folded against the general mass as to be invisible, I have never determined, i 

 Dr. Pringsheim, however, figures them within the cell. I have seen them in i 

 their early development long before motion commenced in them, but they were ., 

 always perfectly formed as soon as apparent. They are present in great numbers, t 

 making a crown or ring around the edge of the transparent beak-like end. "When '■ 

 they commence to vibrate, their action is at first very slow, and the waves of 

 motion run through them deliberately from one cilium to the other, but soon, > 

 however, the motile impulses succeed one another more and more rapidly, until : 

 the general mass of the zoospore begins to tremble, then to rock, and fiuaUy dart- ■' 

 ing oif the little body hastens hither and thither through the water. The zoospore | 

 of an (Edogonium is always readily distinguished from most other similar bodies by 

 its large size and peculiar motion, which is a forward movement combined with a 

 distinct rolling on its long axis. After a time the zoospore, coming in contact 

 with some speck of matter to which it can attach itself, ceases its movements, 

 the cilia rapidly wither away, and the end to which they have been attached 

 swells out or elongates into a broad, or narrow, simple, bifid, or trifid process, 

 placed at an angle to the main axis of the cell, bo as to form the so-called foot, the 

 holdfast that anchors and fixes the new plant. Whilst this is taking place, the 

 general form of the zoospore alters into that of a cylinder, a cellulose wall is 

 secreted all about it, and the first cell of the new plant is complete. As soon as 

 this cell is sufficiently matured, it begins to undergo division in the manner already i 

 described, and to develop into the new filament. 



In regard to the time when these zoospores are given off most abundantly, and 

 the circumstances that influence the process, I can only state that it occurs when 

 there is least tendency to the production of resting spores, probably in youngish 

 plants, and I have thought was favored by a full supply of light, with a moderate 

 temperature. 



Sexual reproduction occurs among the CEdotjouiaccce in accordance with three 

 distinct types, to which the name of monceciotis, dicccious, and gynandrous has 

 been severally applied. The characteristic differences are to be looked for in tlie 

 production of the antheridife or male plant, the female germ being always pre- 

 pared in essentially the same way. In most instances two cells are requisite for 

 the production of the latter. At first there is nothing by which cells set apart for 

 the formation of the female germ can be distinguished from ordinary cells. The 

 proximal one of the pair finally, however, undergoes changes similar to those 

 seen when a zoospore is to be formed, namely, a sort of confusion of the endo- 

 chromc, and finally a gathering of it into a mass at the distal end of the cell. In- 

 stead of there being a solution of the side wall of the cell, however, the end wall 



