METHOD OP OBTAINING DESMIDIE^. 391 



-Those who would wish to know the results of the various 

 operations, should consult the excellent works of M. Trembley 

 and Mr. Baker, which will give them full particulars.* 



Desmidiea. — Another most interesting class of objects for 

 the microscope, but now generally considered as belonging to 

 the vegetable kingdom, are the Desmidiese, a tribe of lowly 

 organized plants, remarkable for the elegance of their form 

 and for being found exclusively in fresh water. They have 

 lately been classified and arranged by Mr. Ealfs in an admi- 

 rable work on the subject, which should be in the possession of 

 every microscopist. As the mode of collecting them differs 

 somewhat from that of the Infusoria, the author has thought 

 proper to borrow Mr. Ealfs' description : — 



" As the Desmidiese are unattached and very minute, they 



are rarely gathered in streams; nevertheless, interesting 



species may occasionally be obtained where the current is so 



sluggish as to permit the thin retaining mucus to elude its 



force. In small shallow pools, that do not dry up in summer, 



they are most abundant; hence pools ia boggy places are 



generally productive. The Desmidieas prefer an open country. 



They abound on moors and in exposed places, but are rarely 



found in shady woods or in deep ditches. To search for them 



in turbid waters is useless ; such situations are the haunts of 



animals, not the habitats of the Desmidieas, and the waters in 



which the latter are present are always clear to the very 



bottom. In the water, the filamentous species resemble the 



Zygnemata, but their green colour is generally paler and 



more opaque. They often occur in considerable quantity, 



and, notwithstanding their fragility, can generally be removed 



by the hand in the usual manner. When they are much 



diffused in the water, I take a piece of linen, about the size 



of a pocket-handkerchief, lay it on the ground in the form 



of a bag, and then, by the aid of a tin box, scoop up the water 



and strain it through the bag, repeating the process as often 



* Memoires pour servir a THistoire cCun Oenre de Polypes cCEau douce. 

 Par A. Trembley, de la Societe Eoyale. A Leide, 1784. — An Attempt 

 towards the Natural History of the Tolype. By Henry Baker, F.R.S. 

 London, 1743. 



