DESMIDS OF THE UNITBD STATES. 



Order, ZYGOSPORE^E. 



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

 into filamentous 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 episporium, 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 terminal growth. Contents of cells (cytioplasni) chloro- 

 plujlom 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. 



