DESMIDS OF THE UNITFD STATES. 



Order, ZYGOSPORE.^. 



Green or brown Algw, unicellular, either free cells or united 

 into filamentou^s fascia. Sexual propagation takes place by an 

 act of copulation followed by conjugation or 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 or 

 triple episjiorium, or membranous envelope. 



In rare cases twin zygospores are developed. 



Family, CONJUGATE. 



Cells free, or united into simple series or filaments ; no branches 

 and no tei'minal growth. Contents of cells (cytioplasm) chloro- 

 phylous green, arranged in parietal bands, axillary lamina, or 

 stellate nuclei. 



Sub-Family or Group, DESMIDIE^E. 



Composed of symmetrical cells, usually constricted in the 

 middle, often of beautiful, ornamental forms, single or conjoined 

 into filiform series, and sometimes involved in a maternal jelly. 

 Asexual multiplication takes place by transverse division, or 

 separation of the semi-cells (Plate XVII, fig. 13 ; Plate XIX, 

 fig. 27) ; and development of new parts similar to the mother 

 semi-cells. 



Copulation takes place between two floating or free cells (Plate 

 XXVII, fig. 27), and produces a zygsopore with a firm middle 

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

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

 one or more regenerated daughter cells. 



