u6 ANNALS OF SCOTTISH NATURAL HISTORY 



R. Kidston and Col. J. S. Stirling, who found this critical 

 plant in the Union Canal near Falkirk. Their attention 

 was first arrested by abnormal forms of P. perfoliatus ; on 

 further examining these a series of variable forms was found, 

 which they were unable to place under any species described 

 in British Floras. These doubtful forms, although of widely 

 different facies, they grouped together, and with excellent 

 judgment labelled " P. perfoliatus x crispus ? " : which, with 

 little doubt, is exactly the parentage of the hybrid named 

 P. undulatus by Wolfgang. 



The two supposed parents were the only Potamogetons 

 found growing with the hybrid form ; except some of the 

 linear-leaved species, which, as Mr. Kidston remarks, " do not 

 affect the plant in question." Messrs. Stirling and Kidston 

 sent all their specimens of the new form to me for examina- 

 tion ; and that no available help might be lacking, they 

 kindly added the whole of therr Stirlingshire collection of this 

 genus a very necessary addition for the investigation of a 

 critical Potamogeton. 



The undulatus forms I found to agree fairly well with my 

 own very extensive series from Mr. E. F. Cooper, collected 

 in Leicestershire, and from Mr. C. R. Billups, collected in 

 Cheshire (described in " Journal of Botany " as P. undulatus, 

 Wolfg. i'. Cooperi mi hi.}, but presenting a sufficient amount of 

 difference to make a further comparison desirable. With 

 this object I then compared the Stirlingshire plant with Wolf- 

 gang's type of undulatus in the National Herbarium at the 

 British Museum, and with the series of " P. perfoliatus v. 

 Jacksoni " ( = P. undulatus var.) in the same collection. Spe- 

 cimen-matching, always difficult in the genus Potamogeton, 

 and especially so in the case of a form which simultaneously 

 produces states resembling crispus, perfoliatus, and nitcns, is 

 not altogether satisfactory ; and is apt to be very misleading. 

 In this instance I found one specimen of the Yorkshire P. 

 Jacksoni to exactly agree with one of the Stirlingshire plant ; 

 but the earlier and the barren states of the two plants did 

 not well correspond. Ultimately I thought it better to refer 

 the new form to the type rather than to either of the already 

 known British varieties. This decision was afterwards con- 

 firmed by further comparison with a specimen of P. undulatus 



