204 FRESH-WATER ALG.E OF THE UNITED STATES. 



perforating the membrane of its host ; extending somewhat 

 beyond, and often widened at its mouth. 



Diameter of cells, about 25 //. 



The only specimens found by myself were in Closterium 

 lunula. They have been found also in other algae. 



Plate CV, fig. 16, five Olpidia in a semi-cell of Closterium. 



OLPIDIUM ENTOPHYTUM, A.Br. 



Parasitic in the interior of plants, perfectly spherical, 

 somewhat smaller than the preceding (intestinum), the tubes 

 perforating the membrane, straight, not inflated, often 

 extending beyond the membrane of the cell they occupy. 



Diameter of cells, 15-20 /*. 



Plate CY, fig. 15, cells of a filament of Oedogonium each 

 containing two plants. 



Diameter of larger cells, 12-15 yw ; smaller ones, 6-10 //. 



Order V. ZYGOSPOREJE. 



An Order composed of green or brownish algse, sometimes 

 single cells, but more frequently series of cells closely united, 

 possessing a peculiar mode of propagation by copulation and 

 conjugation. The contents of two cells, whether individuals or 

 whether in series, flow together and produce a new cell termed 

 a zygospore. As a rule only one, but rarely two zygospores are 

 produced by the copulation of two cells. Sometimes spores are 

 produced without copulation ; such are termed, azygospores. 



Family XVL CONJUGATE. 



Simple filaments composed of a single series of cells, or inde- 

 pendent single cells with chlorophyl-green contents. Chloro- 

 phyl arranged in parietal bands, in axillary laminae, or twin, 

 stellate nuclei. 



SECTION I. ZYGNEME^. 



Cells cylindrical, united into filaments, green, often with a 

 mucous covering, conferva-like. Zygospores are clothed with a 

 triple membrane, the exterior one decidious. When fully 

 developed, after a period of rest, these germinate, putting forth 

 a single germ, in the same way as the seeds of phoeiiogamous 

 plants. This germ elongates by transverse division of the cells. 



