DESMIDS OF THE UNITED STATES. 



Order, ZYGOSPORES. 



Green or brown Algce, unicellular, either free cells <>r united 

 into filamentous fascia. Sexual propagation take- place by an acl 

 of copulation followed by conjugation <>r zygose. Two cells of like 

 appearance are attracted to each other, and unite; the contents of 

 the two cells flow together, commingle, and form a primordial cell 

 called a zygospore ; this develops a double <>r triple episporium, or 

 membranous envelope. 



In rare cases twin zygospores are developed. 



Family, CONJUGATE. 



( fells tree, or united into simple series or filaments ; no branches 

 and no terminal growth. Contents of cells (cytioplasm) chlorophyl- 

 ous green, arranged in parietal bands, axillary lamina, or stellate 



ninlei. 



Sub-Family or Group, DESMIDIE^E 



( fomposed of symmetrical cells, usually constricted in the middle, 

 often <t' beautiful, ornamental forms, single or conjoined into til - 

 form series, and sometimes involved in a maternal jelly. Asexual 

 multiplication takes place by transverse division, or separation of 

 the semi-cells, (Plate XIV, fig. 13; Plate XVI, fig. 27); and de- 

 velopment of new parts similar t<> the mother semi-cells. 



Copulation take- place between two floating or free cells (Plate 

 XXIV, fig. 27) and produces a zygospore with a firm middle 

 membrane, and usually a more delicate inner and miter coating. 

 The zygospore, alter a longer or shorter period of rest, develops 



one or more regenerated daughter cell? 



(21) 



