225 



(Lees), is considered by both authors above mentioned as a 

 hybrid between P. crispus and P. perfoliatus, and as Mr. Fryer 

 has made several accurate experiments of pollinations 1. c, 

 1889, S. 377, this conjecture is no doubt correct. But I cannot 

 agree with the view, that this plant is the same as P. undulatus 

 Wolfg. 



In Lake Constance near Arbon Mr. Ober holze r has 

 found a Potamogeton which in „Fortschritte der schweize- 

 rischen Floristik" 1893 — 95 is determined as P. undulatus 

 Wolfg. A specimen of this plant which is in the Herbarium, 

 called Bodensee-Herbarium, in Zurich has been sent to me 

 through the kindness of Prof. G. Schröter ; it may be P. cris- 

 pus x P. perfoliatus , but it is certainly not P. undulatus 

 Wolfg. Recently a specimen from that locality was sent me 

 from Mr. Oberholzer; it was only P. perfoliatus. 



As P. undulatus always is evidently sterile — Gaspary 

 (1. c. p. 98) says expressly, that the pollen failed — and as I 

 take for granted, that each true species, subspecies or variety, 

 generally set fruit richly, I consider its hybrid nature beyond 

 doubt. I understand it produced by a natural intercrossing 

 between the two species P. crispus and P. praelongus. The 

 relationship with P. crispus is proved by its whole habit, 

 especially by its channelled stem, a character very peculiar 

 for this species, but it differs from it by its strong bushy 

 growth, its bigger stems, its larger, more undulate, but less 

 fringed, dark-green, entire leaves, and its closer and larger, 

 but always sterile spikes. 



The affinity with P. praelongus is proved by the ner- 

 vure of the leaves, the large and more constant ligules on 

 the younger shoots and the entire leaves, but it differs from it 

 in the characters common with P. crispus. This suggestion, 

 which Gaspary already has expressed, has had the best 

 affirmation by an examination by Mr. G. Raunkiær, who 

 accompanied me on my excursion. This examination which 

 will appear in his excellent work entitled „De danske 



Botanisk Tidsskrift. 21. Bind. 15 



