POTAMOGETON UNDULATUS IN STIRLINGSHIRE 117 



gathered by Wolfgang himself, and given to me by my gene- 

 rous friend Dr. Tiselius for the furtherance of this investigation. 

 This latter specimen fortunately presented both the crispus 

 and perfoliatus states of the species, and more closely re- 

 sembles the Stirlingshire specimens than any of the English 

 forms do. Hence I think we may safely add typical P. un- 

 dulatus, Wolfg., to the British Flora. 



P. undulatus may be easily recognised in its ordinary states 

 in living specimens by its compressed stem, like that of P. cris- 

 pus, with foliage somewhat resembling that of P. perfoliatiis ; 

 but the stem-character disappears to a great extent when the 

 plant is dried, and then, in most cases, is only to be detected 

 by the most careful examination. Hence the examination 

 of the fresh stems of doubtful perfoliatus-tor ms is advisable 

 to collectors who wish to find the species in their own locali- 

 ties. It should always be borne in mind, however, that hy- 

 brid forms such as undulatus, decipiens, and nitens are never 

 clearly-defined species like natans and densus, but vary to a 

 considerable extent according to the variation of the species 

 they are bred from, whether induced by local conditions, or 

 inherent variation in the parents themselves. Therefore it 

 will be better for botanists to depend upon a general specific 

 resemblance than upon matching their specimens with others 

 gathered in distant, and often widely different, localities. 



To enable students to recognise the present species, they 

 would do well to consult the original description of Wolfgang 

 in Roemer et Schultes, " Syst. Veget. Mant," ed. 3, p. 259 (re- 

 printed in my note in " Journ. Bot"), and also the excellent note 

 in the "Report of the Botanical Record Club," 1880, p. 150, 

 on " P. perfoliatus v. Jacksoni" by Mr. F. A. Lees. With 

 these and the accurate plate by Mr. R. Morgan which illus- 

 trates the paper in the Journal, no difficulty will be found in 

 naming the species correctly. 



P. undulatus, like many of Wolfgang's proposed species, 

 seems to have escaped the attention of botanists until recently, 

 when the re-discovery of the form by Messrs. Cooper and 

 Hillups led to its recognition as a distinct species, and to a 

 knowledge of its true place in the genus. It had hitherto 

 been placed by many good botanists under P. pr&longus, as 

 an extreme variety. And as this view is entertained to some 

 2 D 



