50 ZYGNEMATACEAE 



When the zygospores are fully mature, an equatorial suture 

 usually can be seen. In many collections the median wall is con- 

 tracted inwardly and the surface thrown into ridges. The ridges 

 are irregular in position and are not morphological features of the 

 wall. They disappear when the spores are treated with dilute 

 potassium hydroxide, while morphological features of the wall 

 become more distinct. 



The species of Zygnemopsis may be distinguished readily from 

 those of Zygnema when in a fruiting condition by the cellulose 

 colloid accumulation in the cells, by the initial very narrow con- 

 jugating tubes, and by the round or quadrangular pillow-shaped 

 spores. They differ from the species of Zygogonium in the form 

 of the chromatophores, the absence of cytoplasmic residues in the 

 gametangia and sporiferous cells, in the form of the spores, and 

 in the stages of tube formation. From the species of Debarya they 

 may be distinguished by the Zygnema-like chromatophores; and 

 from Hallasia by the absence of aplanospores from which one, 

 two, or three sporelings develop. 



Some of the species here classified in the genus Zygnemopsis 

 have been previously placed in the genera: Debarya, Mougeotia, 

 and Zygnema. 



Key to the Species of ZYGNEMOPSIS 



I. Reproducing by aplanospores 12 



I. Reproducing by zygospores, sometimes aplanospores also 2 



2. Diameter vegetative cells mostly less than Sjtt 3 



2, Diameter vegetative cells mostly between 8 and 16 /a 4 



2. Diameter vegetative cells mostly 16 /a or more 11 



3. Median spore wall punctate, yellow, 



diameter vegetative cells 4-6 /a i. Z. silvan gen sis 



3. Median spore wall smooth, golden- 

 brown, diameter vegetative cells 6-7/^'. 2. Z.orientalis 

 3. Median spore wall scrobiculatc, yellow, 



diameter vegetative cells 6-8 /i. 4. Z. floridana 



4. Shorter axis of zygospores less than 32 /i 5 



4. Shorter axis of zygospores 32/i. or more 8 



5. Diameter vegetative cells mostly less than 12/1 6 



5. Diameter vegetative cells mostly more than i2ij- 7 



6. Median spore wall smooth, choco- 

 late brown 5. Z. minuta 



