ON POTAMOOETON FLUITANS. 203 



Moore. — 8. planifolia Hook. Brandon only, Dr. Taylor and W. 

 Wilson. 



Diplophylium obtusifolium Dum. Found more than sixty years 

 ago by Dr. Taylor near Dunkerron. 



Jungermannia Dicksoni Hook. Connor Hill, Dr. Moore. — J. 

 Bantriemis Hook. Brandon, Dr. Moore. — J. Hornschuchiana Nees. 

 Near Upper Lake and Tore Mtn., Killarney, 1869, Dr. Moore. 



Acrobolbus Wilsoni Nees. W. Wilson, 1829; Dr. Taylor, 1841. 



Scalia Hookeri Gray. One solitary female plant on Connor 

 Hill, 1873, Dr. Lindberg. 



Avthoceros lavis L. Abundant near Ventry, Dr. Lindberg and 

 Dr. Moore, 1873. 



ON POTAMOOETON FLUITANS Roth. 

 By William H- Beeby. 



The object of the present paper is to try to throw a little 

 light on the proper application of this name. A good deal that 

 has been written on the subject hitherto seems scarcely more 

 than conjecture ; while a definite statement, like that of Reichen- 

 bach, which surely deserves to be accepted or refuted, or at least 

 to be remarked upon, is passed over in silence. 



The freely-fruiting plant of the Continent, called by many 

 " P. jiuitans," has been assumed to be the plant of Roth ; and this 

 assumption once having been made, fruit is sometimes asked for to 

 prove that any given example is the plant of Roth ! Unfortunately 

 Roth did not describe the fruit at all ; and as it appears to have 

 been impossible to find a type specimen of Roth's plant, the con- 

 ception of the fruit of P. Jiuitans Roth, can scarcely come from an 

 authentic source. As Roth does not give descriptions of the fruit 

 in this genus, the identification of his plant must, in the absence 

 of authentic specimens, rest on other characters and considerations. 



Reichenbach (Ic. Fl. Germ, et Helv., t. 49, 48) figures two 

 plants which he regards as varieties of the same species, viz., his 

 typical sterile P. Jiuitans Roth, in a plate which well represents the 

 British plant ; and his fertile " /3. staynatilis Koch." Speaking of 

 our sterile plant he says, " No one seems to have seen the typical 

 form in fruit, which is known to me in no collection." Now, where 

 there exist two forms, the one fertile and the other sterile, and sup- 

 posed to belong to the same species, the almost universal custom is 

 to call the fertde plant the type ; and it is not likely that Reichen- 

 bach chose the opposite arrangement merely from caprice. The 

 inference is rather that he took the more unusual course because, 

 for some reason known to himself, he felt that he had no choice ; 

 especially when his remarks on the sterility of the typical form arc 

 taken into consideration. And it may be pointed out that the idea 

 of sterility did not altogether originate with Reichenbach, for 

 Chamisso and Schlechtendal say, " Semina, ex Nolte, acutiua 

 carinata quam natantis, attamen nan satis matura observabajitur." 



