66 FRESH-WATEU ALG^ OF THE UNITED STATES. 



tion takes place by zoospores which are evolved in vegetative 

 cells ; two cells separate (v. Plate LXXIII), the chlorophyl con- 

 tained in a membrane, escapes, producing a spherical cell, pro- 

 vided with cilire aro*und a hyaline point, moves about rapidly, 

 then conies to a rest and develops. 



Genus 10, CEDOGONIUM, Lk. 



Filaments simple, articulate. Terminal cell sometimes elon- 

 gated and setiform. Either monoecious or dioecious ; when monoe- 

 cious the oogonia and the sperniogonia cells (antheridia) are on 

 the same filament ; epigynous or hypogynom as the latter are above 

 or below the oogoniuni. Dioecious, when the sperm ogoiiia cells 

 are on different (male) plants. The nannandres are dwarf males 

 somewhat of the form of inverted flasks, the lower part, the 

 stipe, and the upper part consisting of one or more short cells, 

 spermogonia cells (antheridia) ; these dwarf males are located 

 parasitically on or near the oogoniuni, and fertilize it by means of 

 sperrnatozoids developed in the spermogonia cells. Another 

 dioecious form has no dwarf males, but instead, has interstitial 

 spermogonia cells, in independent filaments, like the female 

 plant except usually slightly smaller; these develop and emit 

 the spermatozoids which find their way to the oogonium and fer- 

 tilize the oospore. These two kinds are distinguished, the 

 former as na/nnandrous, and the latter as macrandrous species. 



The dwarf males are supposed to develop from male zoospores 

 (androspores ) and these from small cells similar to the interstitial 

 sperniogonia cells which are found in the filaments of nannan- 

 drous female plants, or in the filaments of independent sterile 

 plants ; the former are called gynandrosporous and the latter 

 idioandrosporous plants. The androsporangia cells and spermo- 

 gonia cells are barely separable when empty, as most frequently 

 found, except by size, the former being usually considerably 

 larger. The androspores are many times larger than the sper- 

 matozoids. 



The fertilization of the oospore is effected through a pore or 

 small spherical opening in the oogonium or through a split in 

 the upper part of the oogonium. In some species the oogonium 

 splits round the top and opens as by a lid. The spermatozoids, 

 having matured and escaped from the spermogonia cells, enter 

 and fecundate the oospore which ripens into a perfect, fertile, 

 resting spore. 



