221 



Potamogeton undulatus Wolfgang 



(P. crispus L. x P. jiraelongus Wulf.). 

 By 



J. Baagø e. 



(With plate 7). 



Un an excursion led by me, in the summer 1895 to 

 the lakes and rivulets of Jutland, a Potamogeton was found 

 in Gudenaa , which in several respects was like P. crispus, 

 but in others diff erred from it. By examination it proved to 

 agree completely with the description of P. undulatus Wolfg. 

 in Roemer and Schult es' Mantissa III, p. 360 ff., a determ- 

 ination which was confirmed by a minute comparison with 

 some original specimens from the Museum of St. Petersbourg, 

 which the late director, Professor Batalin, sent me, and 

 with another specimen which Mr. Bennett most kindly lent 

 to me, all specimens labelled by Wolfgang. 



Description. 



The whole plant is submerged, large and robust, to a 

 length of IV2 meter, the colour dark-green, which gives a 

 dark look to the water, and already at a distance betrays 

 its presence. 



The stem of the spikebearing, full grown plant is big, 

 stiff, a little zigzag lined, brownish-grey, simple below or 

 with only few branches, at the top very branchy, square 



