ZYGNEMACE^. ' 93 



ment, or cells of diflferent filaments. The latter mode of forming a spore is the most 

 usual, whence we have the origin of the names '■'■ Conjugatce" and '■'■ Zygnemece" applied 

 to these Algae, and alluding to their " yoked" character. When two filaments are about 

 to conjugate, they float near one another, lying parallel, or nearly so in the stratum. 

 Then, from the proximate sides of each cell of both filaments there issue short tubes, 

 which mutually unite ; the cell-wall at the point of union disappears, and the contents 

 of both cells are mixed together. Sometimes the whole contents of one cell is discharged 

 into the other, and the spore formed in that cell ; sometimes, and equally commonly, 

 the spore is formed in the connecting tubes. These tubes are sometimes long and 

 barlike ; and the pairs of conjugated threads resemble little ladders. Sometimes they 

 are very short, and the filaments are angularly bent at the point of union. In most 

 cases the spore forms a single spheroidal or angular mass ; but in Thwaitesia it is divided 

 into four sporules, exactly like the tetraspore of one of the Rhodosperms. In the genus 

 CEdogonium, which Mr. Berkeley refers to this Family, the filaments do not conjugate, 

 but the spores are formed by a division of the endochrome of a fertile cell. The cell 

 separates into two half-cells by a transverse partition, as in ordinary cell division ; 

 the spore is then formed in one half ; the other half lengthens to the size proper to the 

 genus and again divides, forming a second spore in one of its halves ; and so it may 

 divide repeatedly until a string of six or eight consecutive spores is formed, in the 

 centre or at the end of the thread, as in (E. monile, a beautiful species from Tasmania- 

 The spores are not always green ; but (especially in (Edogonium) are often brilliantly 

 coloured, orange or vermillion. 



Several genera, containing a large number of species, are described, chiefly from 

 the stagnant or nearly still waters of the Northern Hemisphere. But they are pro- 

 bably dispersed over the globe, though few have yet been brought from the tropics. 

 Unfortunately they do not recover their characters sufiiciently, after having been dried, 

 to admit of being accurately verified from dried specimens : and consequently I am 

 forced to omit specific descriptions of those that I have received from North America. 

 No doubt many of the species of the genera Mougeotia ; Zygnema (Spirogyra) ; 

 Tyndaridea ; Staurocarpus ; and (Edogonium (Vesiculifera) exist in American 

 waters ; but they must be examined on the spot. Mr. Ravenel has kindly sent me a 

 few specimens of Staurocarpus and Zygnema^ but I have not been able to recognize the 

 species satisfactorily. Authors who have written on the subject appear to me to have 

 needlessly multiplied the European species, of which Kiitzing enumerates 200, including 

 58 Zygnemata and as many (Edogonia. 



