DESMIDS. 



Order, ZY< it M'< >l; I Family, I I >NJ1 I i \T.I . 



1 1 1 I > j ~ m 1 1 form :i largi ^roup, nearly cnna] in number of 

 species, t<> thai "I all the nther orders of fresh-water Algce. They 

 are microscopic plants, and are to l<- found Hooting free in |k>1~. 

 ponds :iml sluggish streams in all parte of the world; m I:i-t 

 representatives "I them are t" be met with in ever) clime from the 

 frigid arctic latitudes i" the torrid equatorial Bone ; but unlike the 

 higher orders of plants this wide difference in temperature is not 

 in these Alga always accompanied by corresponding structural 

 difference; for in \<\\ Jersey . varieties have been discovered, which 

 previously wry,- thought to belong exclusively t<> the hottest parte 

 of South America, and in the same State are also found species 

 peculiar to the region of Nova Zembla, and Spitsbergen; we ma} 

 : i -~ ~ 1 1 1 m these latter to have been :i northern legacy t" New Jersey 

 upon the breaking up of what i~ known as the Glacial period, but 

 we have ii" plausible reason t" give for the presence in the same 

 localities of species which are indigenous t" Brazil and the East 

 Indies. In every country however, there are varieties of Desmids 

 that have not been found elsewhere ; a remark which applies 

 peculiarly to the United States, where nearly one hundred species 

 wholly distinct from any heretofore known, have been discovered, 

 and are now for the first time collectively described in this work. 



I lir Desmids are all more or less trelatinous; certain eenera as 

 Hyaiotheca, Desmidium, Sphaerozosma, and some species of Oosma- 

 rium, and of Staurasbrum, have a distinct, wide, colorless envelope ; 

 but the majority are provided with nothing more than an extremely 



thin mucous covering, which, tl gh hardly perceptible under the 



microscope, becomes sufficiently evident in the firmness with which 



