226 



Blomsterplanters Naturhistorie", I here copy in extenso with 



the authors kind permission^). 



„In later years a plant has been found in several places in 



England, which by Eng- 

 lish Botanists is thought 

 identical with F. undula- 

 tus Wolfg. , and which 

 by Mr. Fryer is con- 

 sidered to be P. crispus 

 X P.perfoUatus. The spe- 

 cimens I have had occasi- 

 on to examine, are rather 

 different from our plant 

 as well as from the speci- 

 mens in St. Petersbourg 

 Museum , and several 

 characters seem to prove, 

 that the English plant is 

 really P. crispus x P.per- 

 foUatus, but in that case 

 it is not identical with 

 P. undulatus Wolfg., for 

 the latter agrees per- 

 fectly with the plant 

 found in Denmark, and 

 that is, as we are going 

 to see, without doubt P. 

 crispus X P.praelongus. 

 That P. crispus is the one 

 parent, is evident enough 

 from the form of the 



Fig. 1. 



Transverse section of the stem of: 

 A. Potamogeton praelongus. B. P. cris- 

 pus X P. praelongus (P. undulatus). C. 

 P. crispus. c. axial cylinder; Zfe. vascular 



bundles in the bark; Ig. lacunse. 



*) P. Ascherson and Graebner have adopted my P. undrdatus 

 as P. crispus X P. praelongus in the ^Synojisis der Mitteleuro- 

 paischen Flora" vol. I. 5. Lief., p. 338. And recently Mi'. Fryer 

 has accepted my decision in the Botanical Exchange and Report 

 for 1895 (issued 1897) p. 497. 



