824 ON A NEW HYBRID POTAMOGETON OF THE FLUITANS GROUP. 



of Mepal, Chatteris, and Doddington, all in District 7 of Cambridge- 

 shire, Co. 29. 



By the great liberality of Dr. Gustaf Tiselius, of Stockholm, 

 and of Mr. Charles Bailey, of Manchester, who have kindly lent me 

 two valuable sets of continental " P. fluitans," I have been able not 

 only to compare my series of British fluitans-iorma with those of 

 otber countries, but to obtain a fair notion of what botanists 

 generally mean by " P. fluitans." Amongst the plants sent to me 

 the majority seems to be formed of hybrids of P. nutans crossed with 

 P. lucens, or in some instances, perhaps, with P. ■pohjgonifolius. 

 Of the small minority of more doubtful fluituns -forms, one, P. 

 Illinoensis Morong, belongs to the Zizii section of P. lucens, and the 

 others are freely fruitiug plants, which seem to me specifically 

 distinct from the rest of the group, and which would be more 

 naturally placed between P. natans and P. polygo7iifolius than with 

 a species which so closely approaches P. lucens as P. fluitans of 

 Both. 



Taking the name fluitans as used by botanists, it represents an 

 aggregate as wide as the old P. natans before the segregation of 

 2wlyyonifolius, plantagineus, and fluitans of Nolte. Acting on the same 

 principle as that which seems to have guided Dr. Tiselius in his 

 limitation of the nitens-gi:ou\) (i. e., that all nitens -forms should be 

 hybrids with perfoliatus as one parent), I propose in like manner to 

 restrict the fluitans- group to such forms as are hybrids with P. 

 nutans as one parent ; and to restrict the name P. fluitans Roth to 

 the plant figured by Beichenbach, 'Icones,' f. 88, which plant I 

 have shown in previous notes to be almost certainly P. lucens x 

 P. nutans. 



This, the typical form of the group, agrees well with Roth's 

 original description,- and I follow Reichenbach and Tiselius in 

 considering it to be the form on which Roth founded his species. 

 Nor am I deterred in thus restricting the species by any fear that 

 Roth, or other botanists, may have subsequently described the fruit 

 of other forms supposed to be identical with his original plant. 

 Until a plant agreeing with Roth's description and Reichenbach's 

 figure shall be found in fruit, I consider the supposition that 

 Nolte's species does fruit as having no substantial foundation. 

 That this species may occasionally produce single drupelets fertilised 

 by the pollen of other species I fully admit, but these possibilities 

 are beside the present question, which is : has the plant described 

 by Roth ever been found in a fruiting-state ? It is not a matter of 

 opinion, but a simple matter of fact ; thousands of barren speci- 

 mens are known to exist, but in what herbarium can we find a 

 single fertile specimen ? 



It is true that Dr. Tiselius, whose profound knowledge of the 

 genus Potamuyeton demands the greatest respect, considers a 

 fruiting form found by him in the Neckar, near Heidelberg, to be 

 specifically identical with the plant figured by Reichenbach, 



* See Mr. W. H. Beeby's note in the July number of the current volume 

 of this Journal, p. 203. 



