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II. — Note on Micrasterias americana, Balfs, and its Varieties. 

 By W. M. I^askell, F.R.M.S. 



(Read 14th December, 1887.) 

 Plate II. 



Since the publication of Mr. Ealfs's work on the British Desinidiete, 

 its author must have been pleased to observe the great extension 

 which the study of these beautiful little organisms has received. 

 From 1848 until the present day, scarcely a year has gone by 

 without an increase in the number of species and of the works 

 relating to them, so that in fact the list of writers on desmids is now 

 'quite of respectable, even formidable length, and the study of these 

 plants is getting to be almost as complicated and difficult as that of 

 diatoms. The time has arrived when a comprehensive monograph of 

 the family is not only desirable but necessary. 



The present note has been prepared in anticipation of such a 

 work. Simplification is, I take it, much to be desired in all scientific 

 manuals, and especially so in these days of almost infinite subdivision 

 and specialization of observation. So close and minute is nowadays 

 the examination of the minuter forms of animal and vegetable life, so 

 careful is the diagnosis of each, so numerous are the workers in nearly 

 every branch, that the separation of '-species," "varieties," and "forms," 

 has become almost unbearably multiplied : differences so slight as to 

 be apparent only to the very closest scrutiny are necessarily looked 

 on as sufficient distinctions, and the student is wearied, confused, and 

 perhaps frightened, by the infinite labours entailed upon him. Not 

 only so ; he is also puzzled by the fact (at least in the microscopic 

 forms) that there is no absolute uniformity even in things which he 

 has considered identical. A desmid, for example (I speak from my 

 own observation) kept in a growing cell for some days, will undergo 

 minute changes which it requires a good deal of knowledge of the 



EXPLANATION OF PLATE II. 



iterias americana Ralfs, forma genuina. 

 „ „ „ Integra Turner (forma 6 Kabenhorst). 



recta Wolle. 

 spinosa Turner (MS.). 

 Ralfsii Turner (forma £ Ralfs). 

 major "Wills. 



excelsior Wallich (Turner MS.). 

 Mahahuleshwarensis Hobsorj. 

 Watlichii Grunow. 



WaUkhii forma suecica (Turner MS.). 

 Hermantxianu, Reinsch. 

 fijiensis Macdonald. 

 ampullacea Maskell. 

 ampullacea var. fS Spencer. 



Tbe magaitication of these figures is not uniform, as the object lias only been to 

 exhibit gradations of outline. 



