CHAPTER ONE 



GENERAL TAXONOMIC CHARACTERISTICS 

 The Order ZYGNEMATALES G. M. Smith 1933 



The plants belonging to this order of the Chlorophyta differ 

 from all other green algae in the absence of free swimming flagel- 

 lated gametes and spores; sexual reproduction is consummated by 

 amoeboid gametes through, or within, a tube, pectic sheath, or an 

 enveloping pectic mass. 



The plants consist of single cells, of loose cell aggregates within 

 a pectic gel, or of unbranched or very sparsely branched, and 

 usually undifferentiated, filaments. The cell walls have an outer 

 pectic layer and an inner cellulose layer. The spore walls consist 

 of at least three layers, the inner and outer of which are of cellu- 

 lose, and the median wall of cellulose with varying amounts of 

 chitinous deposits. The median wall may be colored yellow, 

 brown, or blue. 



The chromatophores may consist of axial or parietal plates, or 

 spirally arranged parietal ribbonlike structures, or of two axial 

 stellate bodies often highly diversified among the desmids. 



The zygospores have a dormant period during which there is 

 a fusion of the gametic nuclei followed by a reduction division. 

 At the time of germination the four resulting nuclei may each 

 become the center of a new cell, or two or three of the nuclei may 

 disintegrate and only two or one sporelings emerge from the 

 spore wall. 



The Zygnematales are naturally divided into three families 

 which have, briefly, the following characteristics: 



FAMILY I. ZYGNEMATACEAE 



These are filamentous plants, usually unbranched, and have 

 cylindric cells. The walls of the vegetative cells are unseg- 

 mented and without pores. The chromatophores are either axial 

 more or less stellate, ribbonlike or platelike bodies; or are parietal 

 platelike or spirally arranged ribbonlike bodies. Conjugation of 



