{3) A. BENNETT. POTAMOGETONES OF THE HERBARIUM BOISSIER. 251 



•conparison of fruits) I reported ihe Irish plant to l> r Nyman as Umchites. 

 There is no reasonable doubt thaï M. Fryer in correcl in referring il 

 lo ihe graminifolitu of Fries. And in llie spécimens ifroni Tiickerman 

 himselt') in the Herb. Boissier, il must be confessed thaï lliey are 

 a good deal in habit lake an extreme heterophyllus form. D r Morong 

 was uncertain how to place it, only feeling sure tbat the var lie calls 

 Novaeborac&s, was the saine as the Necker plant of D r Tiselius. and 

 quile believing lhat Chamisso's P. americanus Linnaea 2, 220 was the 

 same. 



What I could say abont il will be found in the Journal of Botany, 297 

 (1893). 



6. P. fluitans Roth F. Germ. 1. 72, 2, 202 (1788). 



The difficulty with this species is; are there two species (or more) pas- 

 sing under this naine, one a possible hybrid that perfecls no fruit (or only 

 so rarely as to be practickly sterile), and the olher that fruits freely and 

 is represenled by D 1 ' Tiselius spécimens from the Necker in Germamy, 

 and Michalet's Jura spécimens. These queries bave been answered in 

 some way by M* Fryer in Journal of Botany 324 (1890) le. 273 (1888) ; 

 M r Beeby Journal of Botany 203 (1890) and by myself in Journal of Bo- 

 tany 295 (1893). 



Still there are a number of herberia spécimens that do not match 

 either of thèse, and the difficulty of whether you hâve before you a non- 

 Iruiting spécimen of the fruiting plant, or only one of the other is great. 

 Spécimens in Herb. Boissier also show a wide différence as to size of 

 fruit, while the variation in the leaves is not great; while it remains 

 certain that there are some spécimens that it is impossible (at least at 

 présent) to seperate where not in fruit by any other character, yet 

 Avhen présent it décides at once, a good exemple is my P. mexicanus. 



D r Schumann in the Flora Basiliensis Fas. 116 (1894) would consider 

 lhat according to habitat, etc.. the vegetative organs mightbe accéléra ted, 

 and no fruit produced, while in others the reverse might occur and 

 fruit be produced; this is of course a difficult idea to combat, as to prove 

 it otherwise, spécimens would need to be taken whence the one was 

 developed. and planted where it was not, and vica versa. 



7. P. occidentalis Sieber (n° 275) ex Cham. Linn. 2. 224 (1827). 

 Another plant that Chamisso considered distinct refered by Kunth 

 natans accantillanus En. 3, p. 128; and by Griesbach F. Brit. West Ind. 

 Islands. 506 (1859) to P. fluitans Rolh. cornes under the fr. form. As do 

 many others described by Chamisso le. 



