No. IO.] FRESH-WATER ALG.E. 55 



Vaucheria D. C. Many filaments growing from one 

 root, green, rather stout. A single filament usually more or 

 less branched, with chlorophyll quite evenly distributed on the 

 inside of the cell wall, forms one plant. Sexual reproduction 

 by oospheres and spermatozoids ; asexual reproduction by 

 zoospores. One zoospore, provided with many cilia, is formed 

 in a swelling at the tip of the thallus, cut off from the rest of 

 the cell by a wall. The oogonia and antheridia, either sessile 

 or on short pedicles, grow in various numbers on the same 

 tube and usually close together. 



V. sessilis (Vauch.) D. C, Figs. 200, 201. Sexual organs 

 of this species are shown in Fig. 206. 



[V. aversa Hass. ; V. geminata (Vauch.) D. C] 



ORDER VIII. CONJUGATE.* 



The Conjugates are green or brownish Algae, sometimes 

 single-celled, but usually composed of many cells closely joined. 

 They are named from the peculiar mode of propagation. Two 

 cells unite their entire contents to form a zygospore ; rarely 

 two zygospores result from such a union. Resting spores or 

 cysts are produced in the Zygnemacece without copulation. 

 Non-motile spores are sometimes formed. All the Conjugates 

 are very slimy to the touch. 



Key to Families. 



Unicellular; cells commonly constructed of two 

 symmetrical halves ; of very many forms, though 

 rarely cylindrical; single, or, very rarely, bound 

 together in a loose thread ; two to eight germs de- 

 velop from a single zygospore desmidiace^e 



Thallus a thread of many similar cells ; each zygo- 

 spore produces only one germ plant zygnemacece 



* Our work upon the remaining orders of Chlorophyceae is as yet quite in- 

 complete. These Algae are abundant in our waters. In the filamentous forms it 

 is difficult or impossible to identify the species from the vegetative stages; and, 

 since in ordinary waters it is usual to find these stages only, specific determination 

 is frequently impossible. The family of Desmidiacea is very abundant; and, 

 while our list contains a large number of them, doubtless a longer study will show 

 many more species. The common species are, however, fairly well represented. 



