231 



Denmark. A. Jutland. As before mentioned in 



1) Gudenaa between Svostrup and Randers 2B h 1895, by 

 the author. 



2) in Allingaa 28 / 7 1895 (Baagøe). 



3) near Randers 9. 1895 (Mr. G. Ostenfeld). 



4) in Østeraa at Aalborg 10 / 8 1895 (Mr. F. Kølpin Ravn). 



5) in Kongeaa between Gredstedbro and Hjortlund 6. 1896 

 (Mr. Raunkiær). 



6) In several places from Foldingbro to Gredsted, especially 

 in abundance near Plougstrupbro 28 h 1896 (Baagøe). 



7) In Nibsaa near Ribe between Vanning lake and Stavn- 

 ager 25 /s 1896 (Mr. Clausen). 



8) In Vanning lake 25 / 6 1897 (Baagøe). 



9) Kongeaa near Villebøl 28 /e 1897 (Baagøe). 



B. Se aland. In Hallebyaa between the outlet in the 

 Great Belt and Augerup Kro 16 / 8 1897 (Baagøe). 



No doubt it may be found in several other places. 



The soil of all the above mentioned localities was sand 

 or gravel, covered with a thin layer of mud. It is found as 

 well in almost stagnant water (Vanning sea) as in running 

 (Hallebyaa) and fast rushing water (Gudenaa at the Kings- 

 bridge). The depth varied from 1- 4 feet, but spikebearing 

 specimens were only found in water 2 — 4 feet deep. 



P. undulatus seldom grows single but in little groups. 

 As P. crispus it has no fixed period for growing, it sets 

 spikes in June, and after August the spikebearing shoots 

 begin to wither, but the rhizome always puts forth new 

 shoots, which all winter keep fresh green on the bottom of 

 the water. Also in outward appearance the young shoots 

 of these plants are very much like those of P. crispus , but 

 the leaves are always entire, not serrulated as in P. crispus. 

 The young plants keep the fine green colour when dried, 

 while the older spikebearing shoots will grow black and 

 fragile. 



Last summer I again visited the above mentioned 



