180 Mr. Hassall's Notices of British Freshwater Alga. 



perform their function by imbibition, which, I beHeve, in my 

 former paj)er I showed to be thoroughly unfounded. 



Your obedient servant, 



J. W. Griffith. 



XXV. — Observations on the genus INIougeotia, on two new Genera 

 of Freshwater Algce, and on Tyndaridea, with desci-iptions of spe- 

 cies. By Arthur Hill Hassall, Esq. 

 [With a Plate.] 

 Genus Mougeotia. 

 The real nature of the genus Mougeotia does not hitherto appear 

 to have been at all understood, and consequently the definitions 

 given of it up to the present time are either erroneous or incom- 

 plete. 



Vaucher thus defines the genus Mougeotia : — " Conjuguees 

 a tuhe inte?-ieur." And Agardh as follows : — " Fila articulata re- 

 ticulata conjuncta, granulis absque ordine dispositis, fructibus in 

 angulis reticuli collocatis." 



The first of these definitions is imperfect, and the second inac- 

 curate, inasmuch as it contains a reference to perfect fructification 

 distinct from the granules or zoospores. 



The true and original species of the genus Mougeotia are all 

 characterized by the singular fact, that sporangia, which Agardh 

 calls the fruit, are never found in them as they are in all other 

 species of the conjugating tribe of Confervse. The filaments do 

 indeed unite, but no transference of the contents of one cell into 

 the interior of the other, and consequently no formation of spo- 

 rangia, ever take place. 



This remarkable circumstance in the history of the genus 

 Mougeotia, resting as it does on long-continued and careful ob- 

 servation of the species composing it, does not admit of the small- 

 est doubt, and although not absolutely stated as a fact, is yet 

 strongly implied by Vaucher in his description of Mougeotia ge- 

 miflexa, in which the follo^^dng observations occur : — 



" This Conjugata has not presented to me the round globules 

 of the other species of the same family; on the contrary, the green 

 matter which it incloses hath appeared to me to present nearly 

 the same form, so that I know not how the grain is formed, nor 

 in what way the development in this species is brought about ; 

 only I have remarked distinctly three or four bright grains im- 

 mersed in this green mattei-, and I have seen in the month of 

 April the cells separate from each other and sink in the water, 

 but I traced them no further. Nevertheless, I have difficulty in 

 believing that the brilliant grains are not the germs. 



" Since writing this description I have seen the germination of 



